Cytoplasmic Inheritance of a Cold-sensitive Mutant in Aspergillus nidulans

Abstract

Cold-sensitive mutants of bacteria are a source of strains defective in the assembly of ribosomes (Guthrie, Nashimoto & Nomura, 1969; Tai, Kessler & Ingraham, 1969). A study of cold-sensitive mutants in Aspergillus nidulans was undertaken in the hope that it would provide ribosomal mutants. Cold-sensitive (cs) mutants were isolated, and when crossed with wild-type the majority of 32 mutants tested segregated as single-gene mutations.One mutant, cs67, showed non-Mendelian segregation of its cold-sensi tive character in such a cross. This paper presents further results demonstrating the extranuclear inheritance of cs67. METHODSThe initial strains of Aspergillus nidulans used in this work were translocation-free. R21 (pabaAr Y A I ) carries the nuclear markers for p-aminobenzoic acid requirement and yellow conidia; ~1 5 3 (wA3; pyroAq) the nuclear markers for white conidia and pyridoxine requirement. RESULTSGrowth properties of cs67. At 37 "C growth of cs67 on solid media is indistinguishable from that of wild-type. The mutant forms only small colonies when incubated at 20 "C.The mutation is not specific to the germination stage since cs67 fails to grow at 20 "C even after an initial overnight incubation at 37 "C. Mutant cs67 does not grow at 20 "C in response to nutritional supplements, nor to molar concentrations of KCl or NaCl.The responses at 37 "C of cs67 to actidione (either 0.1 mg /ml or 2 mg/ml) or sodium deoxycholate (0.08 %) are the same as wild-type.Somatic stability of cs67. When conidia of cs67 were plated and incubated at 37 "C the resulting colonies showed no evidence of vegetative sectoring over several subcultures. Fourteen single-colony isolates from one of these subcultures were tested and all had precisely the same growth properties as the original isolate. Three of these clones (cs67-I, 1x67-2 and cs67-3) were used in the crosses and heterokaryon tests described below, in addition to the original strain (cs67-0).Crosses between cs67 and wild-type. Progeny from individual hybrid perithecia were tested for the segregation of the four nuclear markers and cold-sensitivity. In all cases the nuclear markers segregated as expected, the ratio of mutant to wild-type alleles being I:I (P > 0.05). However, the progeny from any one perithecium were either all cold-sensitive

Cytochrome abnormalities and cyanide-resistant respiration in extranuclear mutants of Aspergillus nidulans

“…The effect of this inhibitor with and without cyanide was tested on exponentialphase mycelium of (+,cs67) grown at 20 C, i.e., when respiration was 100% cyanide resistant. 30 l,0 The results are presented in Table 2. Salicyl hydroxamate alone, added either in ethanol or *ation of (+,+) and as the sodium salt, pH 7.7, did not significantly Total respiration; inhibit respiration at 1 mM.…”

“…We have previously reported isolation of the extranuclear, oligomycin-resistant mutant (oliA1) in the filamentous ascomycete Aspergillus nidulans, which grows slower than the wild-type strain on drug-free media (21), and preliminary results indicated an alteration to its cytochrome spectrum (22). In addition, the extranuclear, cold-sensitive mutant (cs67) has been isolated, which grows at a normal rate at 37 C but markedly slower than the wild-type strain at 20 C (23,30), and the stable recombinant (oliAl,cs67) has been obtained, which grows slower than either of the mutants at 20 C (23).…”

Mitochondrial DNA from Aspergillus nidulans

“…Extranuclear mutants have been isolated recently in the Ascomycete fungus Aspergillus niduluns [ 1,2] , and cycloheximide-resistant incorporation of labelled amino acid into mitochondrial proteins has been demonstrated [3]. Although the size and shape of mitochondrial DNA in yeast [4] and Neuruspora crassa [5,6] has been determined, there has been no similar report for mitochondrial DNA of Aspergillus.…”