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Amongst forty wild strains of Escherichia coli, sixteen utilized galactitol (as did K12) and seven utilized ribitol (as did C) of which six utilized d-arabitol; none utilized all three polyols.
Transduction of genes for ribitol utilization (rtl +) to strains able to utilize galactitol (gat +), whether K12 or wild strains, using wild strains and E. coli C as donors always resulted in loss of the galactitol phenotype. The genes for d-arabitol use (atl +) were always cotransduced with rtl + in interstrain crosses. We confirm and extend the mapping of gat + ( Lengeler, 1977 ) and rtl + atl + ( Reiner, 1975 ) in their respective hosts, K12 and C, by showing both regions to be 50% cotransducible with metG and 3% cotransducible with fpk. In reciprocal transductions, gat + replaced rtl + atl +. In partial diploids, rtl + atl + and gat + regions did not interfere with each other’s expression.
Transfer of rtl + from an Rtl+ Atl− donor by R plasmid (pE10)-mediated conjugation, gave Gat− transconjugants of K12 in which rtl + and a kanamycin resistance gene were 100% cotransducible in the metG region of the chromosome.
It is suggested that the rtl + atl + and gat + 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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