Examination of MLP1 expression in mutants lacking Slt2 activation. (a) Expression of MLP1-lacZ was determined in wild-type and the indicated deletant strains growing to mid-log phase in a rich medium. Each value represents the mean and standard deviation of three independent transformants. (b) Slt2 phosphorylation was examined by immunoblotting total extracts from exponential cultures of the wild-type strain and pmt2 Δ and ssd1 Δ mutants growing in YEPD with an anti-phospho-p44/p42 MAPK antibody. The protein load was monitored using a mouse anti-actin mAb.