Studies on the transcription, translation, and structure of α-actinin in dictyostelium discoideum

Abstract

A clone coding for the F-actin cross-linking protein α-actinin was obtained by screening a genomic library of Dictyostelium discoideum DNA in λgt11 with monoclonal antibodies specific for Dictyostelium α-actinin. The 1.2-kilobase (kb) genomic clone was confirmed as containing part of the α-actinin gene by comparing its nucleotide sequence with the amino acid sequence of tryptic peptides from purified α-actinin. The clone recognized a 3.0-kb message in a Northern blot. Hybridization to RNA isolated from different developmental stages of several D. discoideum strains indicated that the mRNA content increased during early development. A similar result was obtained when the α-actinin content of the cells was followed by Western blot analysis. Hybridization of the clone to DNA from different wild-type strains of D. discoideum indicated a polymorphism on the DNA level that coincided with a polymorphism on the protein level. The data suggest (a) continuous transcription of the α-actinin gene throughout the development of D. discoideum, (b) up- and down- regulation of the levels of α-actinin mRNA and protein with maximum levels at the onset of aggregation, and (c) a high diversity of α-actinin at the DNA and protein level among different D. discoideum strains. The structural data make it conceivable that the highly conserved nature of α-actinin resides only at the functional sites, whereas the helical portions of the α-actinin molecule allow a higher level of diversity throughout evolution.