ACTIN-RELATED PROTEINS IN ANABAENA SPP AND ESCHERICHIA-COLI

Actin has been described in all eukaryotic cells as the major microfil ament cytoskeletal protein. Although prokaryotic cells do not have a c ytoskeleton, proteins related to the latter have been found in differe nt prokaryotic species. We have found prokaryotic actin-related protei ns in the enterobacterium Escherichia coli and in the cyanobacteria An abaena cylindrica and Anabaena variabilis. They were identified by the following criteria: (1) by cross-reaction with a fluorescent conjugat ed anti-actin (rat-brain) mAb by Western blot analysis (in total cellu lar extracts); (2) specific binding of acetone powder and soluble cell ular extracts to DNase I; and (3) specific binding of cells and total cellular extracts to phalloidin. In E. coli, specific binding of phall oidin labelled with rhodamine to cells was detected by spectrofluorome try. In total cellular extracts, three bands of 60, 43 and 35 kDa were weakly recognized by the mAb by Western blot analysis; this recogniti on increased when phalloidin was added to the extracts. Furthermore, t hree polypeptides of 60 kDa were isolated by binding to DNase I, showi ng pI values of 6.7, 6.65 and 6.6, less acidic than all reported actin pi values. In A. cylindrica and A. variabilis, specific binding of ph alloidin labelled with rhodamine to cells was also detected by spectro fluorometry. In total and soluble cellular extracts, the mAb recognize d two bands of 45 and 40 kDa by Western blot analysis, but only the fi rst was purified by binding to DNase I, and it showed three isoforms o f pI values 6.8, 6.5 and 6.4, These results suggest the presence, in p rokaryotes, of proteins with similar biochemical characteristics to eu karyotic actin.