PRECOCIOUS SPORULATION AND DEVELOPMENTAL LETHALITY IN YELA NULL MUTANTS OF DICTYOSTELIUM

A novel developmental gene, yelA, has been found that plays an essenti al role in regulating terminal differentiation of Dictyostelium discoi deum. Strains in which yelA is disrupted by plasmid insertion are arre sted at the tight mound siege but accumulate the bright yellow pigment characteristic of mature sori. Although these mutant strains do not f orm Fruiting bodies, many of the cells encapsulate within the mounds. Sporulation occurs about 6 hours earlier in yelA(-) cells than in wild -type cells, accompanied by precocious expression of a prespore gene, spiA, However, the spores are defective and lose viability over a peri od of several hours. Unencapsulated cells also die unless they are dis sociated from the mounds and shaken in suspension. The yelA gene was i solated by plasmid rescue and Found to encode a protein of 102 kDa in which the N-terminal sequence shows significant similarity to domains Found in the elF-4G subunits of the translational initiation complex e lF-4F. In wild-type cells yelA mRNA first accumulates at 8 hours of de velopment and is maintained in both prespore and prestalk cells until culmination when ii is Found only is stalk cells. Mutations in yelA ca n partially suppress the block to sporulation in mutant strains in whi ch either of the prestalk genes tagB or tagC is disrupted such that an encapsulation signal is not produced. It appears that premature encap sulation is normally inhibited by YelA until a signal is received from prestalk cells during culmination. (C) 1997 Wiley-Liss, Inc.