Genetic mapping of the human and mouse phospholipase C genes

To determine chromosome positions for 10 mouse phospholipase C (PLC) genes, we typed the progeny of two sets of genetic crosses for inheritance of restriction enzyme polymorphisms of each PLC. Four mouse chromosomes, Chr 1, 11, 12, and 19, contained single PLC genes. Four PLC loci, Plcb1, Plcb2, Plcb4, and Plcg1, mapped to three sites on distal mouse Chr 2. Two PLC genes, Plcd1 and Plcg2, mapped to distinct sites on Chr 8. We mapped the human homologs of eight of these genes to six chromosomes by analysis of human × rodent somatic cell hybrids. The map locations of seven of these genes were consistent with previously defined regions of conserved synteny; Plcd1 defines a new region of homology between human Chr 3 and mouse Chr 8. Received: 24 January 1996 / Accepted: 2 April 1996     

Clusters of genes encoding mouse transplantation antigens

We constructed a cosmid library from BALB/c mouse sperm DNA and isolated 64 cosmid clones with cDNA probes for transplantation antigens (class I molecules). Of these clones, 54 mapped into 13 gene clusters containing 36 distinct class I genes and encompassing 837 kilobases of DNA. One gene cluster mapped to the L region and a second cluster with seven genes to the Qa-2,3 region of the major histocompatibility complex. Restriction map and Southern blot analyses suggest that there are subgroups of class I genes. Using a 5' flanking sequence of the L gene as a hybridization probe, we show the L gene to be present in mouse strains expressing this antigen but deleted or mutated in strains failing to express it. Our data suggest that gene duplication and deletion presumably by homologous but unequal crossing-over has altered the size and organization of the class I clusters in different mouse strains and probably is an important mechanism for generating polymorphism in these genes. Analysis of the 36 class I genes with cDNA probes specific for the 5' and 3' ends shows that the exon encoding the third external domain is far more conserved than those encoding the first and second external domains of the transplantation antigen. These differences in variability have interesting functional implications.     

Chromosomal mapping of five mouse G protein gamma subunits

Heterotrimeric G proteins, composed of alpha, beta, and gamma subunits, transduce signals from transmembrane receptors to a wide range of intracellular effectors. The G protein gamma subunits, which play an indispensible role in this communication, constitute a large and diverse multigene family. Using an interspecific backcross panel, we have determined the mouse chromosomal locations of five gamma subunit genes: gamma2, gamma8, gamma10, gamma12, and gammaCone. Combined with previous mapping studies, these data indicate that, with the possible exception of gamma1 and gamma11, the G protein gamma subunit genes are well dispersed within the mouse and human genomes.     

Additional mapping of mouse chromosome 2 genes

The purpose of this work was to elucidate the genetic fine structure of the central portion of mouse chromosome (Chr) 2. Seven Chr 2 congenic mouse strains [B10.PA(L)-pa we un a ^t , B10.PA(L)-pa A ^w , B10.PA(L)-we un a ^t , B10.PA(J)-pa a, B10.FS-we A ^w , B10.C-we A ^w , and B10.YBR-a] were produced. Breeding studies were carried out using strains B10.PA(L)-pa we un a ^t and B10.LP-H-13 ^b to accurately determine the recombination frequencies between marker genes pa and we (1.9%±0.3), we and un (8.8%±0.5), and un and a ^t (4.5%±0.4) of strain B10.PA(L)-pa we un a ^t . These strains and other Chr 2 congenic strains were typed for immunologically defined loci using monoclonal antibody (mAb) C23 reactive with the gene product of B2m ^b T-lymphocyte clone C1 reactive with the gene product of H-3 ^a and H-3 ^c , and lymphocyte clone H1.8 reactive with the gene product of Hd-1 ^a . B2m and H-3 typing located a recombinational event separating [pa B2m H-3] from we (the order of bracketed genes is not known). Hd-1 typing indicated that Hd-1 maps distal to [H-42, H-44] and proximal to un. The gene order [pa, B2m, H-3], we, [H-42, H-45], Hd-1, un, H-13, a ^t , with H-44 mapping centromeric to Hd-1, is indicated by the data. Address correspondence and offprint requests to: R. J. Graff.     

Genetic mapping of Vibrio cholerae enterotoxin structural genes

The structural genes which constitute the cholera toxin operon, ctxAB, were genetically mapped in the Vibrio cholerae El Tor strain RV79. This strain of V. cholerae contains two copies of the ctx operon located on a 7-kilobase-pair tandemly duplicated region. We began by isolating a vibriophage VcA1 insertion mutation in one of the two ctxA genes located in this region. The mutant carrying this ctxA::VcA1 insertion, DC24, was converted to a VcA1-facilitated donor by introduction of the conjugal plasmid pSJ15, which carries an inserted copy of a defective VcA1-like prophage. The donor characteristics of DC24(pSJ15) indicated that the ctxA::VcA1 insertion mutation was near the trp region of the V. cholerae chromosome. Subsequent RV79 three-factor crosses were performed between VcA1-facilitated donors and recipient strains carrying one of two structural gene mutations in ctx, either delta ctxA23P Kmr or delta ctx-7922. The former was constructed by an in vivo marker exchange procedure and could be scored either by its kanamycin resistance phenotype or by its lack of DNA sequences homologous to the ctxA region. The delta ctx-7922 mutation is a total deletion of both ctx copies of strain RV79. The three-factor cross data strongly suggest that the two ctx loci of RV79 map between the nal and his genes of V. cholerae in the trp nal his linkage group. Physical analysis and heterologous crosses between an RV79 El Tor donor and a 569B classical recipient indicates that one of the two 569B ctx operon copies maps in the same region as the RV79 ctx loci (i.e., linked to nal). Together with previously published observations, these data show that the ctx structural genes are not closely linked to other genes known to affect toxin production in V. cholerae.     

Identification and mapping of five new genes in bacteriophage T7

Mutations that affect the single-stranded DNA-binding protein of bacteriophage T7 (gene 2.5) and four T7 proteins of unknown function (the gene 4.3, 4.5, 4.7 and 5.5 proteins) are described and mapped by three-factor crosses. An extensive search for mutants defective in the DNA-binding protein (M_r = 25,562) produced several strains in which this protein has an altered electrophoretic mobility but no strains that appear to lack it completely. The gene 2.5 mutation that was mapped produces a slightly short DNA-binding protein that appears functional by tests in vitro. It seems likely that a functional DNA-binding protein is needed for T7 growth but that conditional-lethal amber mutations in it are rare; the nucleotide sequence known to code for the gene 2.5 protein contains only 1 to 3 sites that would be expected to be readily mutable to conditional-lethal amber codons by N-methyl-N?nitro-N-nitrosoguanidine. The gene 4.3, 4.5 and 4.7 proteins (M_r ～ 8000 to 15,000) are eliminated by a deletion mutant that removes most of the DNA between genes 4 and 5. The gene 5.5 protein (M_r ～ 11,700) is made in relatively large amounts and is affected by two different mutations that were mapped between genes 5 and 6. One of these mutations appears to be an amber mutation that eliminates the protein entirely; the other decreases the electrophoretic mobility of the protein (an apparent increase in size). A larger protein (M_r ～ 18,000), found in small amounts and difficult to observe, is also affected by these two mutations; the relationship of this minor protein to the major gene 5.5 protein is not yet known. The genes 2 and 18 proteins have also been identified in patterns of protein synthesis during infection. The proteins specified by at least 34 different T7 genes have now been identified.