The importance of repairing stalled replication forks

The bacterial SOS response to unusual levels of DNA damage has been recognized and studied for several decades. Pathways for re-establishing inactivated replication forks under normal growth conditions have received far less attention. In bacteria growing aerobically in the absence of SOS-inducing conditions, many replication forks encounter DNA damage, leading to inactivation. The pathways for fork reactivation involve the homologous recombination systems, are nonmutagenic, and integrate almost every aspect of DNA metabolism. On a frequency-of-use basis, these pathways represent the main function of bacterial DNA recombination systems, as well as the main function of a number of other enzymatic systems that are associated with replication and site-specific recombination.     

组合几何学与计算几何学

在过去的几十年里，离散几何逐渐合并，新的学科——计算几何学的出现为那些对几何问题感兴趣的数学家和计算科学家们提供了巨大的动力。本书是这两门学科交叉的自然产物，它包含了32篇论文，内容涉及了这个领域中人们目前感兴趣的广泛课题，如几何排列、多胞形、存储、覆盖、离散凸性、几何学算法及它们的复杂性，还包括了与许多应用领域相关联的低维几何物体的组合复杂性。例如数学规划、可见性问题、运动数据结构和生物化学，还有代数拓扑学、几何概率、实代数几何学及组。     

Effects of weak electromagnetic fields onPhysarum polycephalum: Mitotic delay in heterokaryons and decreased respiration

Summary Continuous exposure ofPhysarum polycephalum to a 75 Hz, 2.0 G, and 0.7 V/m electromagnetic field results in a depressed respiration rate and a lengthening of the mitotic cell cycle. If unexposedPhysarum are mixed with exposedPhysarum the onset of synchronous mitosis in the mixed culture is delayed, occurring at a time between those of the 2 parent cultures.Acknowledgment. This work was supported by the Naval Electronics Systems Command through an Office of Naval Research Contract and a grant from Parkside's Center for the Application of Computers.     

Nucleotide sequence of the gene coding for the major protein of hepatitis B virus surface antigen.

DNA extracted from hepatitis B virus Dane particles has been cloned in bacteria using a plasmid vector. A full-length clone has been examined by restriction endonuclease analysis, and the nucleotide sequence of an 892-base pair fragment from cloned hepatitis B viral DNA encoding the surface antigen gene is reported. The amino acid sequence deduced from the DNA indicates that the surface antigens is a protein consisting of 226 amino acids and with a molecular weight of 25,398. The portion of the gene coding for this protein apparently contains no intervening sequences.     

Some characteristics of the ‘auditory neurophonic’

Résumé Nous avons remarqué dans le système auditif central des ondes qui ressemblent aux ondes microphoniques cochléaires (MC) en imitant étroitement le stimulus. Notre étude montre qu'elles sont d'origine neurale parce que: 1^o) l'amplitude est souvent plus grande en réponse à la stimulation contralatérale au niveau du corps trapézoïde; 2^o) il y a une latence en rapport avec le système auditif examiné; 3^o) une anesthésie progressive cause la dépression de l'onde et finalement sa disparition avec la mort. Nous proposons le terme de phénomene «neurophonique auditif» (NA).

---

---

This study was supported by research grant No. 11250 from the National Institute of Mental Health to N.M.W.

---

NIMH pre-doctoral fellow, No. 5 FO1 MH 30897.     

Synthesis and taste properties of anN-(glucose)-saccharin compound

Résumé La saccharine a été fixée par son azote imidique sur le C₆ du glucose, par l'action de la saccharine sodée sur un dérivé protégé dup-toluénesulfonyl-6-O-d-glucose, et élimination des groupes protecteurs pour former un composé hydrosoluble. La saveur amère peut être attribuée à l'élimination du proton imidique de la saccharine.     

Most of the coding region of rat ACTH beta--LPH precursor gene lacks intervening sequences

The peptide hormones ACTH, beta-endorphin, alpha- and beta-melanotropin(MSH) and possibly gamma-MSH are synthesized in the pituitary gland by the processing of a 32,000-molecular weight (MW) polypeptide called proopiomelanocortin (POMC). The existence of a further precursor (pre form) to POMC containing an additional N-terminal 'leader' peptide has been suggested by analysis of the in vitro translation products of poly(A)-containing RNA from AtT-20 cells, a mouse ACTH-producing cell line of pituitary origin. Nakanishi et al. cloned and sequenced a cDNA copy of the bovine prePOMC mRNA. This sequence confirmed the known structure of the carboxyl half of POMC and revealed the presence of a new MSH-like moiety, gamma-MSH, within the 16,000-MW amino half of the precursor (16K fragment). Recent experiments have suggested that this peptide may act in synergy with ACTH to increase corticosterone and aldosterone production in vivo and in vitro. We have now isolated from a rat genomic DNA library a segment of a DNA encoding most of POMC, using as probe a mouse 144-base pair cloned cDNA fragment encoding beta-MSH and beta-endorphin. The cloned rat gene is one of two (or more) closely related POMC genes. The DNA sequence obtained shows that the cloned POMC gene is not interrupted by any intervening sequence (IVS) between the codon for amino acid 19 and the presumptive poly(A) addition site. This region of POMC encodes all the biologically active peptides mentioned above. The DNA sequence encoding the putative gamma-MSH and the coding sequence that precedes it are highly conserved between rat and cow. This may indicate an as yet unrecognized biological function(s) for the NH2-terminal portion of the 16K fragment.