Haruo Saito

Structure, organization, and somatic rearrangement of T cell gamma genes

We present the initial characterization of a novel family of genes that rearrange in T cells, but do not encode either of the defined (alpha/beta) subunits of the clone-specific heterodimer of the T cell receptor. The family comprises at least three variable (V) gene segments, three constant (C) gene segments, and three junction (J) gene segments. In a cloned cytolytic T lymphocyte, 2C, one of each of these fragments has productively rearranged to yield an expressed VJC transcription unit, which shows no evidence for somatic mutation. Short sequences similar to those implicated in immunoglobulin gene and T cell receptor beta chain gene rearrangement flank the V and J segments of this family. The linkage of two of the three V gene segments has been determined: the segments lie approximately 2.5 kb apart, and are arranged head-to-head. The inverted arrangement may cast light upon the mechanisms utilized by lymphocytes for gene rearrangement.

Initiation of the DNA replication of bacteriophage lambda in Escherichia coli K12

A selective system was designed for the isolation of Escherichia coli mutants which can grow normally at 37 or 42 °C but cannot support replication of bacteriophage λ. One kind of these grp mutants maps at the dnaB locus and the other three kinds map at sites different from all other previously identified dna loci. The grpC, D and E loci map at approximately 0, 71 and 52 to 62 minutes on the E. coli 100-minute map, respectively. The grpC mutation is at a site presently identified as new dna locus (dnaK) by a tsAB756 mutation. In all the grp hosts tested, λ DNA remains superhelical after infection, indicating that the initiation step is blocked. Different classes of λ reg mutants were isolated which are able to replicate either in some or in all grp hosts. Two reg mutations were mapped and found to be located within the ori-O-P region of the λ genome. Some reg mutant phages showed simultaneous temperature sensitivity in their growth on grp+ cells. Both the temperature sensitivity and the reg character were found to be caused by a single mutation in the P gene. Moreover, λ phages harboring typical π mutations in the P gene (Georgopoulos & Herskowitz, 1971) can multiply on some of the grp mutants, and some of the reg mutant phages can replicate on the groP mutant cells. The grp mutations are recessive to grp+ but reg mutations are dominant over reg+ in all cases studied. The present data are consistent with the replisome model in which several gene products participate in the replication apparatus.