Abstract
T YPICAL Salmonella strains are “diphasic” with respect to their flagellar antigens. That is, they manifest one of two genes, H, or H,, but not both in a given clone until a phase variation takes place and the alternative antigen is expressed. The genetic analysis of this alternation by transductional methods (LEDERBERG and EDWARDS 1953; LEDERBERG and IINO 1956) has shown that the variation depends on a “change of state” at the H, locus. The alternating factor has not been separated by recombination from the determinant for antigenic specificity of H,. On the other hand, repeated cycles of alternation in state have occurred at H, without influencing its antigenic specificity. The H, gene, the determinant of the antigen of the alternative phase, is not linked to HZ, but the expression of H, depends on the inactive state of H,. The present paper is part of a comprehensive study of the genetics of Salmonella phase variation (IINO 1958; 1961a,b). Various anomalies, or exceptions to the simple pattern of diphasic variation have occurred, whose assimilation to the general scheme can throw light on the genie control of protein synthesis. The anomaly presented in this paper is represented by CDC-157, a strain of Salmonella paratyphi B, now much used as an antigen for the production of diagnostic anti-12 antiserum (EDWARDS and BRUNER 1942). The advantage of CDC-157 for this purpose is its apparent monophasic behavior; that is, large clones will consist nearly exclusively of cells whose flagellar antigen is 1.2. A genetic analysis of this strain has revealed two anomalies: ( 1) The 1.2 antigen is determined by an allele at the H, locus instead of the H, usual for this antigen, and (2) the stock is carrying a duplicate H, locus. The genotypic formula of CDC-157 is thus HlbH,‘.P, by contrast to the genotype HIbHB1.* for typical strains of S. paratyphi B. These genotypes accurately summarize the genetic behavior of the respective strains.
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