Novel RING Finger Proteins, Air1p and Air2p, Interact with Hmt1p and Inhibit the Arginine Methylation of Npl3p

Abstract

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are involved in the mRNA processing and export and are post-translationally modified by methylation at arginine residues in their arginine-glycine-rich (RGG) domains. We screened the factors that can interact with the RGG domain of Npl3p only in the presence of Hmt1p with the two-hybrid system in Saccharomyces cerevisiae. An isolated clone, YIL079, encodes a novel RING finger protein that was not directly bound to Npl3p but associated with the N terminus of Hmt1p. Thus, we designated the gene product Air1p (arginine methyltransferase-interacting RING finger protein). Air1p inhibited the Hmt1p-mediated methylation of Npl3p in vitro. Overexpression of Air1p repressed the Hmt1p-dependent growth of cells. Since homology searches indicate that the YDL175 gene product has significant identity (45%) with Air1p, we designated the gene AIR2. Air2p also has a RING finger domain and was bound to Hmt1p. Although single disruption of either gene gave no effect on the cell growth, cells lacking Air1p and Air2p grew at an extremely slow rate with accumulated poly(A) ؉ RNA in the nucleus. Thus, Air1p and Air2p may affect mRNA transport by regulating the arginine methylation state of heterogeneous nuclear ribonucleoproteins.

Air1 Zinc Knuckles 4 and 5 and a Conserved IWRXY Motif Are Critical for the Function and Integrity of the Trf4/5-Air1/2-Mtr4 Polyadenylation (TRAMP) RNA Quality Control Complex

“…Air1 and Air2 are functionally redundant because air1⌬ and air2⌬ single deletion mutant cells grow similarly to wild type cells, but air1⌬ air2⌬ double mutant cells exhibit a strong growth defect (45). Both Air1 and Air2 copurify with Trf4, but only Air1 copurifies with Trf5 (14,(21)(22)(23).…”

“…The screen was performed in cells deleted for both AIR1 and AIR2 because air1⌬ or air2⌬ single deletion mutants showed no significant growth defects, but an air1⌬ air2⌬ double deletion mutant exhibited a severe growth defect compared with wild type cells (Fig. 1C) (14,45). This screen led to the identification of an air2 mutant containing a single cysteine to arginine amino acid change in the second cysteine of zinc knuckle 5 (air2-C167R) that showed significantly impaired growth at 37°C (Fig.…”

“…, and CUTs, such as NEL025c, in S. cerevisiae (14,21,22,45). Air1 and Air2 are functionally redundant because air1⌬ and air2⌬ single deletion mutant cells grow similarly to wild type cells, but air1⌬ air2⌬ double mutant cells exhibit a strong growth defect (45).…”

“…Air1/2 proteins contain five adjacent CX 2 CX 4 HX 4 C zinc knuckles (ZnK1-5; Fig. 1A) that could interact with nucleic acids or bind protein (22,45). In retroviral nucleocapsid proteins, one or two CX 2 CX 4 HX 4 C zinc knuckles form metalcoordinated reverse turns that typically contact viral singlestranded tetraloop RNA via the variable (C)X 2 and (H)X 4 residues (14,22,47,48).…”

A Proteomic Analysis of Arginine-methylated Protein Complexes

“…The ZNF9, RING zinc finger protein 9, was identified by LC/MS/MS, and the presence of RG repeats in its sequence suggests that it is a direct epitope of SYM10. The function of ZNF9 is unknown, but it is a nucleic acid-binding protein with an AIR1 (arginine methyltransferase-interacting protein 1) domain (62). The presence of CCTG repeats in intron 1 of ZNF9 gene leads to myotonic dystrophy type 2 (63).…”