SUMMARY: Amongst forty wild strains of , sixteen utilized galactitol (as did K 12) and seven utilized ribitol (as did C) of which six utilized D-arabitol; none utilized all three polyols.

Transduction of genes for ribitol utilization ( ) to strains able to utilize galactitol ( ), whether K12 or wild strains, using wild strains and C as donors always resulted in loss of the galactitol phenotype. The genes for D-arabitol use ( ) were always cotransduced with in interstrain crosses. We confirm and extend the mapping of (Lengeler, 1977) and (Reiner, 1975) in their respective hosts, K12 and C, by showing both regions to be 50% cotransducible with and 3% cotransducible with In reciprocal transductions, replaced . In partial diploids, and regions did not interfere with each other's expression.

Transfer of from an Rtl Atl donor by R plasmid (pE10)-mediated conjugation, gave Gat transconjugants of K12 in which and a kanamycin resistance gene were 100% cotransducible in the region of the chromosome.

It is suggested that the and genes (or parts of them) act as alternative, or mutually exclusive, regions in the chromosome. Possible reasons for the existence of alternative characters are discussed.


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