SUMMARY: A temperature-sensitive mutant strain of has been isolated which failed to grow normally on minimal agar medium at 43 °C unless mannose was supplied as a sole carbon source. The mutant has been given the symbol for mannose relief. Under restrictive conditions (43 °C) the mutant produced extensive areas of swollen hyphae, called balloons, and wall preparations from cultures grown at 40 °C had approximately one-third of the mannose found in walls of control cultures. The strain produced a more thermolabile phosphomannose mutase than the wild-type strain, so it is suggested that the mutation is in the structural gene coding for this enzyme.

The strain failed to grow on minimal agar medium containing 0·1% (w/v) mannose and 0·9% (w/v) glucose at 43 °C. This property was used to obtain revertants, one of which was a double mutant . Growth of the double mutant in media containing [14C]mannose at 43 °C showed that 84% of the label found in the wall occurred in mannose in comparison with 33% in the wild-type control. Autoradiography of cultures of the double mutant using [H]mannose showed predominant incorporation of label into the tip region of growing hyphae. A strain, isolated following haploidization of a diploid, was unable to grow on media containing glucose or mannose alone. The strain had reduced phosphomannose isomerase (EC activity. The mutation, which is epistatic to , has been located to linkage group VIII and the mutation to linkage group V. A pathway is presented for the utilization of mannose in .


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