Nucleotide sequence and developmental expression of Acanthamoeba S-adenosylmethionine synthetase gene

Transcription by RNA polymerase II during Acanthamoeba differentiation

The rates of transcription of several protein coding genes during Acanthamoeba differentiation have been examined by nuclear run-on and RNase protection assays. During early encystment, transcription by RNA polymerase II increases approximately 4-fold, whereas transcription by RNA polymerases I and III is decreased, as previously described. The rates of transcription from a wide variety of individual genes are only slightly affected during the first 16 h of encystment, although profilin gene expression is markedly increased. The levels of mRNAs encoding TPBF, TATA binding protein, cyclin-dependent kinase, protein disulfide isomerase, profilin, myosin II heavy chain, ubiquitin and extendin are stable during mature cyst formation, whereas mRNAs encoding actin, S-adenosyl methionine synthase and tubulin are substantially decreased in abundance within 16 h of starvation-induced encystment. We conclude that in contrast to the negative regulation of large rRNA and 5S rRNA synthesis during differentiation, the RNA polymerase II transcription apparatus is not negatively regulated. Control of Acanthamoeba differentiation is likely to be mediated by positive regulation of genes necessary for cyst maturation.

Structure and expression of a cyst specific protein of Acanthamoeba castellanii

The life cycle of Acanthamoeba is divided into a growth-division phase and two distinctive processes of cellular differentiation, termed encystment and excystment. Polyacrylamide gel electrophoresis revealed that a specific protein of 21 kDa in molecular weight occurs in the cyst, but not in the trophozoite stages of A. castellanii Neff strain. This cyst-specific protein, designated as CSP21, was purified from guanidine-HCl extract of cyst wall and anti-CSP21 antibody was produced. Immunoblotting of proteins extracted from a variety of species of Acanthamoeba genus suggested that the antibody is specific for group II amoebae, therefore, providing a useful tool for Acanthamoebae taxonomy. A cDNA clone for A. castellanii CSP21 was isolated by immunoscreening of a cDNA expression library constructed from mRNA of amoebae at encysting stage. The deduced primary structure indicated that CSP21 is a hydrophilic protein showing no significant homology with peptides thus far published. RNA blot analysis showed that the expression of CSP21 mRNA was restricted within early stages of encystment, suggesting that the biosynthesis of CSP21 is regulated at mRNA level.