Abortive intermediates in transcription by wheat-germ RNA polymerase II. Dynamic aspects of enzyme/template interactions in selection of the enzyme synthetic mode.
At constant enzyme concentration and with the full set of nucleotide substrates dictated by template sequence, the chain-length distribution of polymeric product varies with template concentration in reactions catalysed by wheat-germ RNA polymerase II. Under the same conditions, but in the presence of a single ribonucleoside triphosphate, the rate of condensation of the triphosphate substrate to a dinucleotide primer also exhibits a complex dependence with the template concentration. This effect is observed using poly[d(A-T)] as a template. For both reactions there are two extreme types of behaviour in each of which transcription appears to involve a single enzyme synthetic mode, characterized by either a high (at low template concentration) or a low (at high template concentration) probability of releasing the transcripts. A strong correlation is found between these two pathways, such that conditions favouring the abortive release of trinucleotide products in the single-step addition reaction are associated with the synthesis of short-length RNA species in productive elongation, and reciprocally. A model previously developed by Papanicolaou, Lecomte & Ninio [(1986) J. Mol. Biol. 189, 435-448] to account for the kinetics of polymerization/excision ratios with Escherichia coli DNA polymerase I, and by Job, Soulié, Job & Shire [(1988) J. Theor. Biol. 134, 273-289] for kinetics of RNA-chain elongation by wheat-germ RNA polymerase II provides an explanation for the observed behaviour with the plant transcriptase. The basic requirement of this model is a slow equilibrium between two states of the polymerization complex with distinct probabilities of releasing the product. In the presence of Mn2+, and under conditions allowing the synthesis of poly[r(A-U)], one of these states is involved in the formation of oligonucleotides shorter than 15 bases, whereas the other catalyses the polymerization of chains longer than 40 bases.
de Mercoyrol
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Centre de Biochimie et de Biologie Moléculaire, Centre National de la Recherche Scientifique, Marseille, France.
Soulié
J M
JM
Job
C
C
Job
D
D
Dussert
C
C
Palmari
J
J
Rasigni
M
M
Rasigni
G
G
D004247:DNA / Q000235:genetics; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009843:Oligoribonucleotides / Q000096:biosynthesis / Q000378:metabolism; D011063:Poly A-U / Q000378:metabolism; D012319:RNA Polymerase II / Q000235:genetics*; D013698:Templates, Genetic; D014158:Transcription, Genetic / Q000502:physiology*; D014908:Triticum / Q000235:genetics*
D009843:Oligoribonucleotides; D011063:Poly A-U; C053104:uridylyl-(3'-5')-adenylyl-(3'-5')uridine; D004247:DNA; D012319:RNA Polymerase II; D008274:Magnesium