Thymidine kinase-deficient mutants of Physarum polycephalum; relationships between enzyme activity levels and ploidy

Thymidine (TK) and deoxycytidine (dCK) kinase levels, chromosome counts and whole culture protein:DNA ratios have been determined in the TK- plasmodial strains of P. polycephalum--TU84 and TU63--and on several wild type (wt) plasmodial and amoebal strains from Wis 1 and Colonia backgrounds. It was found that (a) dCK levels and protein:DNA ratios were similar in all plasmodia, regardless of ploidy or genetic background; (b) TU84 and 63 were haploid; (c) TK specific activity was similar in all wt plasmodia but lower in amoebae; (d) TK activities of mutants and wt were approximately additive in heterokaryons. It was concluded that TK deficiency is due to a defect in a structural gene and that wt strains are TK+/TK+ and mutants hemizygous TK-.