Some observations concerning sp and ure-2 in Neurospora

F.J. Bowring & D.E.A. Catcheside - School of Biological Sciences, Flinders University, G.P.O. Box 2100, Adelaide, South Australia, 5001.

We are currently seeking rec-2 which is proximal to am on linkage group V and are gleaning incidental information on genes in this region and elsewhere. So far, the following is apparent:

sp is recessive: each of 15 heterokaryons forced between his-3 K874; sp B132 and am1 32213 strains by growth on Vogel's + glycine medium had wild-type morphology.

The gene order sp, ure-2, am inferred from two point crosses is confirmed by three point data: FGSC 3809 (a; ure-2 D74) was crossed to F11089 (A; sp B132, am B501). 320 random spores were isolated, 79% germinated.

  Zygote genotype 

       and 

recombination percent  Parental combinations   Singles Region I   Singles Region II

sp    +      am         sp + am   + ure-2 +   sp ure-2 +  + + am  sp + +   + ure-2 am

+   ure-2    +           135        92           9          11       5           0

  7.9      2.0

A gene in FGSC 4299 interferes with Kolmark's urease test: While seeking to order sp, ure-2 and am, we set up a cross between FGSC 4299 (a; ure-2 47, am 32213) and T9043 (A; his-3 K874; sp B132) . Of 320 random spores , 92% germinated and were scored for urease activity by dabbing conidia onto paper soaked in urea and a pH indicator to detect ammonia production (Kolmark 1969, Mutation Res. 8:51-63). By this test, T9043 was urease positive and FGSC 4299 urease negative. However, only 23% of the progeny were urease positive, suggesting the segregation of a second mutation unlinked to ure-2. There is preliminary evidence that this additional locus could be linked to his-3.