PROTEIN SUBSTRATES FOR CGMP-DEPENDENT PROTEIN-PHOSPHORYLATION IN CILIA OF WILD-TYPE AND ATALANTA MUTANTS OF PARAMECIUM

In the ciliated protozoan Paramecium, swimming direction is regulated by voltage-gated Ca2+ channels in the ciliary membrane. In response to depolarizing stimuli, intraciliary Ca2+ rises, triggering reversal of the ciliary power stroke and backward swimming. One class of Ca2+-unresponsive behavioral mutants of Paramecium, atalanta mutants, cannot swim backward even though they have functional Ca2+ channels in their ciliary membrane. Several atalanta mutants were characterized with regard to several Ca2+-dependent activities, but no significant difference between wild type and the mutants was detected. However, one allelic group, atalanta A (initially characterized by Hinrichsen and Kung [1984: Genet. Res. Camb. 43:11-20]), showed a helical swimming path of opposite handedness from that of wild-type cells when detergent-permeabilized cells (''models'') were reactivated with MgATP. When cGMP-dependent protein kinase purified from wild-type cells was added to atalanta A models, the handedness of the swimming path was reversed. Cyclic GMP stimulated in vitro phosphorylation of several proteins in isolated cilia, and the pattern of phosphoproteins was very similar for wild type and atalanta mutants, with one exception: a protein of 59 kDa was phosphorylated much less in the mutant ata A. When ciliary proteins were separated by gel electrophoresis and then phosphorylated ''on blot'' by purified cGMP-dependent protein kinase, phosphoprotein patterns were similar in wild type and ata mutants except that a 48 kDa protein (p48) from ata A(3) was more heavily phosphorylated. This difference in p48 phosphorylation was also observed with cGMP-dependent protein kinase purified from ata A(3) mutant cells. Ciliary p48 may be part of the mechanism that regulates the orientation of the ciliary power stroke. (C) 1995 Wiley-Liss, Inc.