Template specificity of DNA-dependent RNA polymerase I and II for synthetic polynucleotides during development of the cellular slime mold Dictyostelium discoideum.

The template specificity of DNA-dependent RNA polymerases I and II (ribonucleoside 5'-triphosphate : RNA nucleotidyltransferase [EC 2.7.7.6]) of Dictyostelium discoideum was investigated with several synthetic polynucleotides at three different stages of development. Both the enzymes exhibited several common characteristics for some templates, and distinctly different properties for other ones. Of single-stranded homopolymers, the strands of pyrimidine nucleotides were much transcribed in the order of poly(dC) greater than poly(dT). The double-stranded homopolymers, poly(dA). poly(dT)) and poly(dG).poly(dC) were transcribed asymmetrically, the pyrimidine-containing strand being preferentially read. Transcription of double-stranded alternating copolymers, poly([d(A-T)].poly[d(A-T)] and poly[d(G-C)].poly[d(g-C)] occurred to some extent. Except for poly(rC), all of the single-stranded ribonucleotide homopolymers were extremely poor as templates. The polynucleotides containing thymidine were more efficient templates for polymerase I than polymerase II. The enzyme activities of the two polymerases were more or less variable with some polynucleotides among three stages of development, suggesting the possibility that D. discoideum RNA polymerases tend to change their template specificity during development.