Updating the rna polymerase ctd

The carboxyl-terminal domain (CTD) of RNA polymerase (pol) II comprises multiple tandem repeats with the consensus sequence Tyr(1)-Ser(2)-Pro(3)-Thr(4)-Ser(5)-Pro(6)-Ser(7) that can be extensively and reversibly modified in vivo.

Our experiments established that () Ser5(P)-Pro6 comprises an essential two-letter code word that is read chiefly by the m RNA capping apparatus.We refer to this junctional segment to the body of Rpb1 as the CTD “rump.” Distal to the rump is an array of 25 heptad repeats that adhere perfectly to the YSPTSPS consensus, with the single exception of an alanine in lieu of Pro3 in the fifth heptad downstream of the rump.We reported previously that a CTD composed of the rump plus 12 or more native heptads sufficed for normal growth of mutants are viable, signifying that phenylalanine is functional in lieu of Tyr1 and that Ser5 is the only strictly essential phosphorylation site in fission yeast.We also exploited our collection of CTD mutants to query whether and how perturbations of CTD primary structure affect CTD serine phosphorylation patterns in vivo, as gauged by Rpb1 reactivity with phospho-specific antibodies.We found that Ser2 phosphorylation does not rely on Ser5, Pro6, Ser7, or Thr4, whereas Ser5 phosphorylation does not depend on Ser2, Thr4, or Ser7.

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