Gene organisation, sequence variation and isochore structure at the centromeric boundary of the human MHC.

We have mapped and sequenced the region immediately centromeric of the human major histocompatibility complex (MHC). A cluster of 13 genes/pseudogenes was identified in a 175 kb PAC linking the TAPASIN locus with the class II region. It includes two novel human genes (BING4 and SACM2L) and a thus far unnoticed human leucocyte antigen (HLA) class II pseudogene, termed HLA-DPA3. Analysis of the G+C content revealed an isochore boundary which, together with the previously reported telomeric boundary, defines the MHC class II region as one of the first completely sequenced isochores in the human genome. Comparison of the sequence with limited sequence from other cell lines shows that the high sequence variation found within the classical class II region extends beyond the identified isochore boundary leading us to propose the concept of an "extended MHC". By comparative analysis, we have precisely identified the mouse/human synteny breakpoint at the centromeric end of the extended MHC class II region between the genes HSET and PHF1.     

Acetamide Agar for Differentiation of Nonfermentative Bacteria

An acetamide agar medium is described for use in the differentiation of nonfermentative gram-negative bacteria. With few exceptions, indicator reactions were rapid, intense, and clear-cut.     

Inhibition of primase, the dnaG protein of Escherichia coli by 2'-deoxy-2'-azidocytidine triphosphate.

2'-Deoxy-2'-azidocytidine-5'-triphosphate was investigated as an inhibitor in two reconstructed enzyme systems which catalyze the replication of two viral DNAs. During replication of the duplex replicative form of phiX174 DNA, DNA polymerase III holoenzyme was weakly inhibited and inhibition was reversed by dCTP. A more pronounced inhibition, not reversed by either dCTP or CTP, was observed during replication of the single-stranded DNA of the bacteriophage G4, a close relative of phiX174. This effect depended on the incorporation of 2'-deoxy-2'-azidocytidine-5'-triphosphate by primase (dnaG protein) which synthesizes a 29-residue RNA primer at the unique origin of bacteriophage G4 DNA replication. Extension of the primer strand, terminated by 2'-deoxy-2'-azidocytidine-5'-triphosphate is then severely inhibited. Primase was also inhibited by the 2'-deoxy-2'-azido derivatives of ATP, GTP, and UTP.