A temperature independent mutation at the rib-1t locus in Neurospora crassa.

NLY two riboflavin mutants have been described so far in Neurospora crassa, 51602t(rib-I) (MITCHELL and HOULAHAN 1946) in linkage group VI, and Y30539 (rib-2) (GARNJOBST and TATUM 1956) in group IV. MCNUTT and FORREST (1958) list two other riboflavin mutants which were used in testing their pteridine derivative from Eremothecium as a growth substance. One of these is 76R5 (C168, METZENBERG, personal communication, 1961). The other, C107, a riboflavin-requiring poky mutant, was sent to us from the California Institute of Technology collection by W. S. MCNUTT, who obtained negative results in cross-feeding experiments between this strain and the two known riboflavin strains (personal communication, 1954). Since no report of the genetics of C107 (r ib-3) has appeared in the literature, it has seemed worthwhile to describe the brief study made in this laboratory. To free the new strain from the poky character, C107a was first crossed with a St.L wild type A, and several fast-growing (i.e., at rate of wild type) riboflavinrequiring reisolates selected for further study. One of these, C107-l(5-5) a, was crossed with SY7A wild type. All of the germinants of the two crosses which failed to grow in minimal medium at 31°C required riboflavin for growth also at 25°C. Table 1 shows the growth response of one riboflavin reisolate from the cross with SY7A in a series of increasing amounts of riboflavin in minimal medium at three temperatures, 25"C, 30°C and 34°C.