The 5' ends of Drosophila heat shock genes in chromatin are hypersensitive to DNase I

Many specific sites in Drosophila chromatin are hypersensitive to DNase I. The positions of such sites were mapped along the regions of the genome coding for two heat shock proteins. Such sites lie at the 5' ends of heat shock genes and may function as elements for recognition by molecules which regulate gene activity.     

Depletion of the predominant B-cell population in immunoglobulin mu heavy-chain transgenic mice

The transgenic mouse line M54 was generated by introducing a functionally-rearranged immunoglobulin mu heavy-chain gene into the germ line of a C57B1/6 inbred mouse. Previous examination of the antibodies produced by B-cell hybridomas derived from transgenic M54 mice showed that the presence of the mu transgene grossly altered the immunoglobulin repertoire of unimmunized animals, suggesting that these mice suffer from a serious immunoregulatory perturbation. Studies presented here introduce a new perspective on this functional defect. We show that the lymphoid tissues from these transgenic mice lack virtually all conventional bone-marrow-derived B cells, which constitute the predominant B-cell population in normal mice and which typically produce primary and secondary antibody responses to T-cell-dependent antigens. Moreover, the bone marrow from transgenic M54 mice is depleted of pre-B lymphocytes, indicating a serious defect in early B-cell lymphopoiesis. In contrast, CD5 (Ly-1) B cells, a second B-cell population displaying a characteristic set of cell surface markers which are derived from distinct precursors in the peritoneum, are represented at normal frequencies in these transgenic mice. Thus, the presence of the rearranged immunoglobulin heavy-chain transgene in M54 mice results in an unexpected selective developmental defect that impairs the development of bone-marrow-derived pre-B and B cells without affecting Ly-1 B cells.     

Contribution of immunoglobulin heavy-chain variable-region genes to antibody diversity

A mouse cloned cDNA probe containing a variable (V) region belonging to the VHIII subgroup has been used in filter hybridisations to estimate the number of heavy-chain V-genes in this subgroup of mouse and human DNA. There seem to be about 10 and 20 VH-genes hybridising to this probe in mouse and human DNA, respectively. Studies of cross-hybridisation of the related VK-genes from MOPC21 and MPC11 myelomas indicate that the experiments detect all members of the VHIII subgroup.     

Identification of D segments of immunoglobulin heavy-chain genes and their rearrangement in T lymphocytes

The finding that the diversity (D) and joining (JH) but not the variable (VH) DNA segments of mouse immunoglobulin heavy-chain genes are joined in the DNA of some cloned cytolytic T cells, led to identification and sequencing of three different D DNA segments. Two segments identified on the embryo DNA carry on both the 5' and 3' sides two sets of characteristic sequences separated by a 12-base pair spacer, which have been implicated as recognition signals for a recombinase. The third segment, identified in a form joined with a JHDNA segment in a T cell, carries the recognition signal on the 5' side. These results support the 12/23-base pair model for somatic generation of immunoglobulin V genes, and rule out the possibility that the cytolytic T cells use assembled VH, D and JH sequences to encode their antigen receptors.     

Two protein-binding sites in chromatin implicated in the activation of heat-shock genes

The resistance to exonuclease digestion of two regions of chromatin at the 5' end of heat-shock genes in Drosophila implies they have protein bound to them. The pattern of resistance before and after induction of gene expression suggests that heat-shock genes are activated by the sequential binding of at least two protein factors.     

UV light-induced immunoglobulin heavy-chain class switch in a human lymphoblastoid cell line

During attempts to select nonsecretory variants from 0.467.3, and Epstein-Barr virus-transformed human lymphoblastoid cell line that secretes small amounts of IgM lambda, we exposed the cells to UV light. Cells that survived the irradiation were subcultured and their supernatants were screened for immunoglobulin production by an enzyme-linked immunosorbent assay (ELISA). Although stable nonsecretory variants were not isolated, we report here that an immunoglobulin class switch occurred in the UV-treated cell population. All survivors were found to produce large quantities of IgG lambda. Some cell cultures also produced the original IgM lambda. The UV-light-induced class switch was regularly reproducible with this target cell line.     

Unusual sequences in the murine immunoglobulin mu-delta heavy-chain region

The delta heavy (H) chain of mouse immunoglobulin D (IgD) is unusual both in its structure and in its differential expression relative to immunoglobulin M (IgM; reviewed in ref. 1). The region of DNA between IgM and IgD H-chain constant-region genes is probably implicated in this control. So far only fragments of the area have been sequenced. Now, however, we present the complete sequence as well as the sequence of the introns of the C delta gene. We have found several interesting features (Fig. 1), including an open reading frame (ORF) between Cmu and C delta which encodes 146 amino acids that might represent a previously unsuspected domain-like protein; three blocks of simple repetitive sequences; a 162-base pair (bp) unique-sequence inverted repeat; and a domain-like pseudogene in the large intron of C delta. We have not found, however, any sequence 5' of C delta resembling the switch (S) recombination sequences associated with class switching in other heavy chains. Moreover, we have determined the 3' deletion end point of an IgD-producing myeloma and find no sequences reminiscent of switch sites nearby.     

Sequences at the somatic recombination sites of immunoglobulin light-chain genes.

The entire nucleotide sequence of a 1.7-kilobase embryonic DNA fragment containing five joining (J) DNA segments for mouse immunoglobulin kappa chain gene has been determined. Each J DNA segment can encode amino acid residues 96--108. Comparison of one of the five J DNA sequences with those of an embryonic variable (V) gene and a complete kappa chain gene permitted localisation of a precise recombination site. The 5'-flanking regions of J DNA segments could form an inverted stem structure with the 3'-non-coding region of embryonic V genes. This hypothetical structure and gel-blotting analysis of total embryo and myeloma DNA suggest that the somatic recombination may be accompanied by excision of an entire DNA segment between a V gene and a J DNA segment. Antibody diversity may in part be generated by modulation of the precise recombination sites.     

Identification of reciprocal translocation sites within the c-myc oncogene and immunoglobulin mu locus in a Burkitt lymphoma

The association between certain human tumours and characteristic chromosomal abnormalities has led to the hypothesis that specific cellular oncogenes may be involved and consequently 'activated' in these genetic recombinations. This hypothesis has found strong support in the recent findings that some cellular homologues of retroviral onc genes are located in chromosomal segments which are affected by specific tumour-related abnormalities (see ref. 4 for review). In the case of human undifferentiated B-cell lymphoma (UBL) and mouse plasmacytomas, cytogenetic and chromosomal mapping data have identified characteristic chromosomal recombinations directly involving different immunoglobulin genes and the c-myc oncogene (for review see refs 5, 6). In UBLs carrying the t(8:14) translocation it has been shown that the human c-myc gene is located on the region of chromosome 8 (8q24) which is translocated to the immunoglobulin heavy-chain locus (IHC) on chromosome 14. Although it is known that the chromosomal breakpoints can be variably located within or outside the c-myc locus and within the IHC mu (refs 9, 11) or IHC gamma locus, the recombination sites have not been exactly identified and mapped in relation to the functional domains of these loci. We report here the identification and characterization of two reciprocal recombination sites between c-myc and IHC mu in a Burkitt lymphoma. Nucleotide sequencing of the cross-over point joining chromosomes 8 and 14 on chromosome 14q--shows that the onc gene is interrupted within its first intron and joined to the heavy-chain mu switch region. This recombination predicts that the translocated onc gene would code for a rearranged mRNA but a normal c-myc polypeptide.     

Identification and nucleotide sequence of a diversity DNA segment (D) of immunoglobulin heavy-chain genes

A putative diversity segment of immunoglobulin heavy-chain genes (D segments) has been identified 700 base pairs 5' to JH1 DNA on the germ-line genome of the mouse. This 10-base pair D segment is flanked by two sets of sequences related to (SEE FORMULAR IN TEXT) which are possible recognition sites for a recombinase. The spacer separating the heptamer and the nonamer is 12 base pairs long on both sides of the D segment. As the space separating the two signal sequences in VH DNAs and JH DNAs is 23 +/- 1 base pairs long, the two recombinations required for creation of a complete immunoglobulin VH gene, a VH--D joining and a D--JH joining, follow a 12/23-base pair spacer rule. Allelic exclusion is discussed with respect to D segments.     

Dispersed human immunoglobulin kappa light-chain genes

The gene segments encoding the constant and variable regions of human immunoglobulin light chains of the kappa type (C kappa, V kappa) have been localized to chromosome 2. The distance between the C kappa and V kappa genes and the number of germline V kappa genes are unknown. As part of our work on the human V kappa locus, we have now mapped two solitary V kappa gene and a cluster of three V kappa genes to chromosomes 1, 15 and 22, respectively. The three genes that have been sequenced are nonprocessed pseudogenes, and the same may be true for the other two genes. This is the first time that V-gene segments have been found outside the C-gene-containing chromosomes. Our finding is relevant to current estimates of the size of the V kappa-gene repertoire. Furthermore, the dispersed gene regions have some unusual characteristics which may help to clarify the mechanism of dispersion.     

Variable amplification of immunoglobulin lambda light-chain genes in human populations

The human lambda immunoglobulin locus displays a series of restriction fragment length polymorphisms that are readily detected in small populations of normal individuals. Similar polymorphisms appear in populations of wild mice, suggesting that the lambda locus is subject to rapid variation within a single species. Here we show that the polymorphisms seen in the human lambda locus seem to have arisen from unequal meiotic crossing over, altering the number of lambda from as few as six to as many as nine per haploid genome. This expansion and contraction in the number of human lambda genes is significant in that it may affect an individual's capacity to produce variation among lambda light chain genes.