Updating the rna polymerase ctd

By contrast, yeast strains with alanine inserted between Ser7 and Tyr1 in every other heptad were viable (15), as were strains within alanine inserted between Tyr1 and Ser2 of every other heptad (7), implying that the ), signifying that the essential CTD information is indeed contained within a diheptad repeat.

updating the rna polymerase ctd-38updating the rna polymerase ctd-39

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.

repeats of the RNA polymerase II carboxyl-terminal domain (CTD) convey information about the transcription apparatus—a CTD code—to a large ensemble of CTD-binding receptor proteins.

Four of the seven coding “letters” of the fission yeast CTD (Tyr1, Pro3, Ser5, Pro6) are essential in vivo, but the grammatical rules of the code are obscure.

For example, the heptad elements in different registers: one site binds TSPSYSP, whereas the other engages SYSPTSP (14).

This observation led to the clear prediction that the “functional unit” of the CTD must comprise more than one tandem heptad to satisfy the requirements of the many cellular CTD-binding proteins.

We also undertook a “thought experiment” to see whether genetics could assign an essential CTD coding “letter” to a specific CTD–receptor pair in the sea of available cellular receptors, by attempting to bypass the requirement for that letter by delivering a cognate receptor protein to the Pol II transcription complex via other means.

Translating the thought into action, we were able to override the requirement for Ser5, and Ser5 phosphorylation, by fusing an essential cellular Ser5-PO receptor—the m RNA capping enzymes RNA triphosphatase and guanylyltransferase—to the carboxyl terminus of the otherwise nonfunctional Rpb1-CTD-S5A protein (10).

The instantaneous primary structure of the CTD provides informational cues about the state of the transcription machinery—a CTD code—that is “read” by CTD receptor proteins (3).

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