In Salmonella typhimurium, UV-irradiation of the histidine-deficient mutant hi-31 induced a slowly growing reversion to histidine-independence. This formed colonies much smaller than wildtype. By means of transduction the newly created character “small colony” was proved to be heritable. As demonstrated by the following experiments this was due to an independant suppressor-mutation (S-31). After UV-irradiation of hi-31/S-31 a small fraction of cells forming large colonies, revealed growth-characteristics of wildtype. After transduction of small colony type cells by phages raised on wildtype the same large colonies were obtained. Expected to be of genotype hi-31+/S-31, they were used as donor for transduction of hi-31. Both, large colonies (hi-31+/S-31) and small colonies (hi-31/S-31) were isolated, which proved to be stable in further transfers.26 histidin-requiring mutants, belonging to 4 groups, each of them characterised by the same block in histidine synthesis, were transduced with phage raised on hi-31/S-31. None of them exhibited changes of growth characteristics, resulting from the incorporation of the suppressor-gene. Thus the suppressor S-31 turned out to be pseudoallel-specific.This result is considered as evidence that pseudoalleles of the histidine series in Salmonella typhimurium not only are units of recombination but also of function of genetic material. The differences between levels of functions exhibited by units which have been called pseudoalleles by various investigators are discussed in connection with the gene concept.
Expression of Drosophila Rrp1 protein in Escherichia coli. Enzymatic and physical characterization of the intact protein and a carboxyl-terminally deleted exonuclease-deficient mutant.
