CDNA CLONING OF PHYSARUM-POLYCEPHALUM DNA TOPOISOMERASE-I AND EXPRESSION ANALYSIS IN PLASMODIA TREATED WITH CAMP

cDNA encoding DNA topoisomerase I from Physarum polycephalum was isola ted from a poly(A)(+)-primed library (3'-region) and by PCR (5'-region ). The coding region of cDNA was 3045 bp, encoding a polypeptide of mo lecular mass of 112 kDa. Identity between predicted amino acids sequen ces of conserved domains and corresponding domains from another eukary otic type I DNA topoisomerases varied from 33.2 to 53.5% for the core domain and from 33.8 to 57.4% for the C-terminal domain. A peculiar fe ature of Physarum DNA topoisomerase I was a stretch of repeated KPAX.. .X motifs in the N-terminal domain of the polypeptide. Although treatm ent of the plasmodia with db-cAMP increased relaxing activity of the D NA topoisomerase I severalfold, there was only a slight increase in th e mRNA level. (C) 1998 Elsevier Science B.V.