P62 a new class of ubiquitin binding protein binds to rna and associates with active ribosomes

p62 is a novel cellular protein widely expressed in many tissues, p62 was initiallaly identified as a phosphotyrosine independent ligand of lck-SH2 domain and later shown to interact with ubiquitin non-covalently. To identify potential interactors of p62, we have used the yeast two-hybrid system to screen Hela eDNA library, p62 specifically interacted in vivo and in vitro with two ribosomal proteins L40 and 26. Biochemical analysis showed that p62 associates with polysomes and also with 40S subunit, p62 association with polysomes was susceptible to RnaseA treatment, which disrupts polyribosomes but was resistant to high salt treatment, which preserves polysome structure. Furthermore, p62 binds to RNA in in vitro binding assays with specificity to poly(G) RNA. The zinc finger domain of p62 alone is sufficient for RNA binding. P62 is phosphorylated during GO exit and such phosphorylation is rapamycin sensitive. Interaction of p62 with ribosomal proteins,RNA, 40S subunit, association with polysomes and rapamycin sensitive phosphorylation indicates potential function of p62 in translational regulation. This study was supported by grants NIH GM 4896 and ACS CN84478.