Different postsynaptic events in two types of retinal bipolar cell

The first synapse in the vertebrate visual system is made between the photoreceptors and the biopolar cells. Bioplar cells fall into two distinct classes according to whether the cell hyperpolarizes or depolarizes to small centred spots of light. Most evidence indicates that the light-induced hyperpolarization of the photoreceptprs suppresses transmitter release from the synaptic terminals, and it is probable that the differences between the two bipolar cell classes results from the different actions of the photoreceptor transmitter. In analysing the membrane potential fluctuations in both types of bipolar cell we find that the voltage noise spectra differ. It is to be expected that postsynaptic noise would be composed of the sum of noise generated in and transmitted from the cones and the noise arising from the statistical nature of synaptic transmission. We report here evidence for two such components in the voltage noise spectra recorded from each type of bipolar cell. The differences in the frequency distribution of the presumed transmitter-related components indicates that the transmitter generates events of longer duration in the depolarizing biopolar cells.     

The joining of V and J gene segments creates antibody diversity

The variable regions of mouse kappa (kappa) chains are coded for by multiple variable (V) gene segments and multiple joining (J) gene segments. The V kappa gene segments code for residues 1 to 95; the J kappa gene segments code for residues 96 to 108 (refs 1-3). This gene organisation is similar to that encoding the V lambda regions. Diversity in V kappa regions arises from several sources: (1) there are multiple germ-line V kappa gene segments and J kappa gene segments; (2) combinatorial joining of V kappa gene segments with different germline J kappa gene segments; and possibly, (3) somatic point mutation, as postulated for V lambda gene segments. Also, from a comparison of the number of germ-line J kappa gene segments and amino acid sequences, it has been suggested that J kappa region sequences may be determined by the way V kappa and J kappa gene segments are joined. This report supports this model by directly associating various J kappa sequences with given J kappa gene segments.     

Left-handed Z-DNA is induced by supercoiling in physiological ionic conditions

In physiological ionic conditions (200 mM NaCl), the (dC-dG)16 and (dC-dG)13 blocks in plasmid pRW751 are in a left-handed state when the negative superhelical density of the plasmid is greater than 0.972. As the salt concentration decreases or when (dmC-dG) sequences are present, less negative supercoiling is required to induce the right- to left-handed DNA transition. Furthermore, the single strand-specific nuclease, S1, recognizes and cleaves aberrant structural features at the junction between neighbouring right- and left-handed DNA regions.     

Amplification of immunoglobulin lambda constant genes in populations of wild mice

The lambda immunoglobulin light chain (Ig lambda) locus of BALB/c inbred mice consists of two variable region gene segments (V lambda)1-3, and four constant region gene segments (C lambda)1,2,4,5. Each C lambda gene segment is associated with a unique joining segment (J lambda)2,4-7, and they are organized in two paired units, J3C3-J1C1 and J2C2-J4C4 (refs 4, 8). Using cDNA probes specific for C lambda 1 and C lambda 2 (ref. 9) we have analysed the genomic organization of the C lambda gene segments in wild-derived and inbred strains of mice. Although Southern blots of the genomic DNA of inbred mice show a constant pattern of hybridization, wild-derived mice show a high degree of variation in the number, size and intensity of hybridizing fragments. We have now found that, per haploid genome, mice of a Mus musculus musculus stock isolated from Sladeckovce, Czechoslovakia (CzII) have at least 12 C lambda segments, and mice of a Mus musculus domesticus stock 'Centreville Lights' from Centreville, Maryland (CL) have at least 8 C lambda segments. There appears to have been relatively recent amplifications of the C lambda gene segments in wild mice.