Four enzymes involved in ribonucleoside and deoxyribonucleoside catabolism (deoxyribose-5-P aldolase, thymidine phosphorylase, phosphodeoxyribomutase, and purine nucleoside phosphorylase) are coded for by four closely linked structural genes on the Salmonella chromosome. The genetic order of these genes is (deoC-deoA-deoB-deoD)-serB-thr. Studies on polarity mutants and induction patterns indicate that the deoB and deoD genes may constitute a single operon and that the deoC and deoA genes may constitute a second closely linked operon.

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Summary Morphological studies of metaphase chromosomes were done with rats derived from the BIL/1 strain, which has genes affecting growth and reproduction linked to the major histocompatibility complex by conventional Giemsa‐trypsin staining and the results were compared to rat strains not carrying these defects. A subterminal‐terminal centromeric polymorphism was detected in chromosome 3 [del 3 (pter → cent)] among the strains studied. Comparison of the G‐banded karotypes of the rats carrying the defects with the karotypes of the otsher strains did not reveal any gross chromosomal abnormalities.

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