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Systematic name YGR156W
Gene name PTI1
Feature type ORF, Verified
Coordinates Chr VII:800546..801823
Primary SGDID S000003388

Description of YGR156W: Essential protein that is a component of CPF (cleavage and polyadenylation factor); involved in 3' end formation of snoRNA and mRNA; interacts directly with Pta1p; has similarity to mammalian Cleavage-Stimulation Factor CstF-64[1][2][3]


Community Commentary

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PTI1 is an essential gene involved in the coupling of Pol II transcription to pre-mRNA 3' processing (cleavage and polyadenylation). It was first described genetically as a supressor of cold sensitivity resulting from deletion of CTK1 (CTK1 encodes the catalytic subunit of CTDK-I, which hyperphosphorylates the CTD of the largest subunit of Pol II). Temperature sensitive mutations of PTI1 are synthetically lethal with CTK1 deletions , and with a t.s. allele of RNA14, a component of cleavage factor IA, which cleaves pre-mRNA prior to 3' polyadenylation. CF IA is the apparent yeast homolog to mammalian CstF, with Rna14p showing sequence similarity to CstF-77. Both Rna15p (a known component of CF IA) and Pti1p have sequence similarities to CstF-64. Combining t.s. alleles of PTI1 and RNA15 shows slight growth defects, but no lethality.

A known example of PTI1 and 3' pre-mRNA processing is the aberrant 3' cleavage of NCE102 in a strain with a t.s. allele of PTI1. In this strain, 3' cleavage occurs at multiple sites - two sites that are used in wild type strains, and at least one downstream site (160-180nt past the usual cleavage site) that is not detectably used in wild type strains. The CTK1 knockout strain shows a similar effect on 3' cleavage site usage for the NCE102 transcript.

Pti1p binds both Rna14p and Pta1p, the yeast homologs of mammalian CstF-77 and symplekin, which both bind CstF-64 (for which RNA15 and PTI1 are likely homologs). PTI1 also binds Pcf11p, a component of yeast CF IA that binds Rna15p. Pti1p binding to these proteins is almost entirely by a central region with homology to the "hinge" region of CstF-64 that is responsible for most of CstF-64's protein-protein interactions.

The genetic interactions of CTK1 and PTI1, and the similar effects of ctk1 and pti1 t.s. on NCE102 processing indicate that the phospho-CTD generated by CTDK-I is involved in bringing 3' cleavage factors to their targets, and that a complex containing Pti1p is thus recruited.

It has been hypothesized that given these properties of PTI1 and Pti1p, that it is a component of an alternate form of CF IA, substituting for Rna15p. Given the similarities of their bindings, and the non-lethality when t.s. alleles of PTI1 and RNA15 are combined, it is unlikely that Rna15p and Pti1p coexist in the same complex. Given the poor conservation of yeast 3' processing signal sequences, this hypothesis proposes that alternate forms of CF IA exist to recognize different 3' cleavage-polyadenylation signals.



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  1. Dheur S, et al. (2003) Pti1p and Ref2p found in association with the mRNA 3' end formation complex direct snoRNA maturation. EMBO J 22(11):2831-40 SGD PMID 12773397
  2. Dichtl B, et al. (2002) A role for SSU72 in balancing RNA polymerase II transcription elongation and termination. Mol Cell 10(5):1139-50 SGD PMID 12453421
  3. Skaar DA and Greenleaf AL (2002) The RNA polymerase II CTD kinase CTDK-I affects pre-mRNA 3' cleavage/polyadenylation through the processing component Pti1p. Mol Cell 10(6):1429-39 SGD PMID 12504017

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