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Biomedical subjects

P Berg

Publications and source records attributed to P Berg.

At least 307 records · Page 17Linked to original sources
PubMed1969

Recessive lethals: a new class of nonsense suppressors in Escherichia coli.

Two new nonsense suppressors in Escherichia coli were found in partial diploids carrying F'14 and were shown to be on the episome. These suppressors can exist only in cells which also contain the su(-) allele, i.e., su(+)/su(-) heterozygotes. Presumably the mutations cause an alteration of an essential cellular component, the complete loss of which is lethal. Su7, an amber suppressor, has an efficiency of 76 per cent and su8, an ochre suppressor, an efficiency of 4 per cent.

Alleles↗
PubMed1969

Transduction of merodiploidy: induced duplication of recipient genes.

Escherichia coli PB160, which carries a tandem duplication with the gene order metB(+)argH(-)su(159) (+)thi(+): metB(+)argH(+)su(159) (-)thi(+), was used to study the mechanism of P1 transduction of genes in the duplicated region. Transduction of the su(159) (+) allele contained within the duplicated segment yields two kinds of su(159) (+) recombinants: 91% are haploid su(159) (+) and 9% are su(159) (+)/su(159) (-) merodiploids. The duplication in these merodiploid transductants includes the metB locus; however, both copies of the metB locus usually are derived from the recipient. Thus, the requirements for transduction of the "condition of merodiploidy" appear to be the cotransduction of the repeat point (the region where the duplication begins to repeat itself) and, of course, the selected marker (in this case su(159) (+)). A mechanism whereby two recipient chromosomes interact with the transduced "repeat point" region to regenerate the tandem duplication is implicated. It appears that a duplication much larger than the quantity of genetic material carried by a P1 phage can be produced in a transductant.

Chromosomes, Bacterial↗
PubMed1968

T4 bacteriophage mutants suppressible by a missense suppressor which inserts glycine in place of arginine for the codon AGA.

Phage mutants of T4 have been isolated which can multiply only on Escherichia coli strains which contain a missense suppressor which is known to cause the substitution of glycine for arginine in response to the AGA codon. Mutations producing the suppressible phenotype were mapped and shown to occur in six different phage cistrons. Two of the cistrons were concerned with deoxyribonucleic acid synthesis, two were concerned with phage structural components, and two were concerned with functions required for growth in E. coli K-12 but not in E. coli B. The burst size of the different phage mutants grown on strains carrying the same suppressor was dependent upon the efficiency of suppression, which in turn is known to be dependent upon the glycyl-transfer ribonucleic acid synthetase activity.

Arginine↗