A rat histone H4 gene closely associated with the testis-specific H1t gene

A rat histone H4 gene closely associated with the testis-specific H1t gene was isolated by screening the Sargent-Bonner rat genomic library using cloned human histone genes as probes. Both the H4 gene and the H1t gene are located on a 7-kb EcoRI genomic DNA fragment. Although the deduced amino acid sequence of the rat H4 histone is identical to that of the sequence of human histone H4, the nucleotide sequence of the coding region differs significantly from the coding region of the human H4 gene. Moreover, the relative spacing between the 5'-consensus sequence elements is unique for an H4 gene. S1-nuclease protection analyses reveal that both the H4 and H1t mRNA species are present in a fraction of rat testis cells highly enriched in pachytene spermatocytes, while only the H4 mRNA species is present in a rat myeloma cell line (Y3-Ag1.2.3). During a 1-h hydroxyurea treatment of the Y3 cells, which produces a 99% inhibition of DNA synthesis, the level of this H4 mRNA drops by only 50%, indicating that the stability of this mRNA is only partially coupled with DNA synthesis.

Studies on insulin degradation inside the pancreatic B-cell: evidence for a regulating role of glucose

The present study aimed at testing whether insulin degradation inside the pancreatic B-cell is regulated by insulin release or by glucose per se. Radioactively prelabelled isolated rat islets were cultured in unlabelled medium for 24 h. During that chase period the media contained (a) 50 or 300 mg glucose/dl alone or (b) together with 100 micrograms diazoxide/ml and (c) 50 mg glucose/dl without or with 10 mM L-leucine or 300 mg glucose/dl. The content of labelled (pro-)insulin in islets and media was measured and related to degradation. No degradation was found at the high glucose concentration, not even when insulin release was blocked by diazoxide. Degradation was also inhibited in the presence of leucine. The results suggest that glucose per se or its metabolism prevents insulin from being degraded inside the B-cell.