The Y-box binding protein 1 (YB-1, YBX1) is a member of the family of DNA- and RNA-binding proteins with an evolutionarily ancient and conserved cold shock domain. It falls into a group of intrinsically disordered proteins that do not follow the classical rule 'one protein-one function' but introduce a novel principle stating that a disordered structure suggests many functions. YB-1 participates in a wide variety of DNA/RNA-dependent events, including DNA reparation, pre-mRNA transcription and splicing, mRNA packaging, and regulation of mRNA stability and translation. At the cell level, the multiple activities of YB-1 are manifested as its involvement in cell proliferation and differentiation, stress response, and malignant cell transformation. WIREs RNA 2014, 5:95-110. doi: 10.1002/wrna.1200 CONFLICT OF INTEREST: The authors have declared no conflicts of interest for this article. For further resources related to this article, please visit the WIREs website.

The mammalian Y-box-binding protein 1 (YB-1), also known as p50, dbpB, MSY-1, and EF1A, is a member of the multifunctional family of DNA/RNA binding proteins with an evolutionarily conservative cold-shock domain (26). Some prokaryotic members of this protein family were identified as major cold-shock proteins, because their synthesis is strongly enhanced by decreasing temperature, and they serve for bacterial adaptation to growth at low temperature (15).Upon binding to DNA, YB-1 functions as a transcription factor and regulates expression of genes with a Y box in their promoters (34). In addition, YB-1 is involved in reparation (17, 21) and, probably, in replication of DNA (16). Through interaction with mRNA nuclear precursors, this protein participates in alternative splicing of mRNA (5, 33). In the cytoplasm, YB-1 serves as the main mRNA packaging protein (31) and regulates the life time (11) and mRNA template activity in protein synthesis (13,23).YB-1 has a dual effect on protein synthesis depending on the YB-1/mRNA ratio. At a low ratio typical for polysomal mRNPs, YB-1 stimulates translation at the stage of initiation (12,23,29). At an increased ratio corresponding to free mRNPs, YB-1 inhibits the protein synthesis both in vitro (23, 24) and in vivo (7) at the very beginning of translation initiation by displacing the translation initiation factor eIF4G from mRNA (24).At the cellular level, YB-1 increases cell resistance to ionizing radiation and DNA-damaging chemicals; it can serve as an early marker of multiple drug resistance and induces resistance to oncogenic transformation by the phosphatidylinositol 3-kinase/Akt-kinase pathway (1, 19). The above data suggest that the nucleocytoplasmic distribution of YB-1, as well as its content within the cell, should be under strict control.Recently, we have found a regulatory element within 3Ј untranslated region (UTR) of YB-1 mRNA that specifically interacts with two major proteins of cytoplasmic mRNPs, the poly(A)-binding protein (PABP) and YB-1. As a result, PABP selectively activates translation of YB-1 mRNA, irrespective of whether or not it has a 3Ј poly(A) tail (32).Here, we have analyzed the YB-1 effect on YB-1 mRNA translation. It was found that YB-1 can completely suppress its own synthesis at low concentrations that have a stimulating effect on translation of other mRNAs. The inhibition occurs at or prior to joining of the 40S ribosomal subunit to YB-1 mRNA. We have mapped the YB-1 and PABP binding sites on the regulatory element of YB-1 mRNA and have shown that YB-1 binds to two sequences (nucleotides [nt] 1133 to 1145 and 1165 to 1172) containing the same 8-nt motif (UCCAG/ ACAA), and PABP interacts with an A-rich sequence of about 50 nt in length (nt 1149 to 1196). The binding sites of YB-1 and PABP overlap, and these two proteins compete for binding to the regulatory element of YB-1 mRNA. In addition, PABP can restore the translation of YB-1 mRNA inhibited by YB-1. MATERIALS AND METHODSPlasmid construction. The pBluescript II SK YB-1 construct cont...

RNA-binding proteins are of vital importance for mRNA functioning. Among these, poly(A)-binding proteins (PABPs) are of special interest due to their participation in virtually all mRNA-dependent events that is caused by their high affinity for A-rich mRNA sequences. Apart from mRNAs, PABPs interact with many proteins, thus promoting their involvement in cellular events. In the nucleus, PABPs play a role in polyadenylation, determine the length of the poly(A) tail, and may be involved in mRNA export. In the cytoplasm, they participate in regulation of translation initiation and either protect mRNAs from decay through binding to their poly(A) tails or stimulate this decay by promoting mRNA interactions with deadenylase complex proteins. This review presents modern notions of the role of PABPs in mRNA-dependent events; peculiarities of regulation of PABP amount in the cell and activities are also discussed.

Y-box binding proteins (YB proteins) are DNA/RNA-binding proteins belonging to a large family of proteins with the cold shock domain. Functionally, these proteins are known to be the most diverse, although the literature hardly offers any molecular mechanisms governing their activities in the cell, tissue, or the whole organism. This review describes the involvement of YB proteins in RNA-dependent processes, such as mRNA packaging into mRNPs, mRNA translation, and mRNA stabilization. In addition, recent data on the structural peculiarities of YB proteins underlying their interactions with nucleic acids are discussed.

The major protein of cytoplasmic mRNPs from rabbit reticulocytes, YB-1, is a member of an ancient family of proteins containing a common structural feature, coldshock domain. In eukaryotes, this family is represented by multifunctional mRNA/Y-box DNA-binding proteins that control gene expression at different stages. To address possible post-transcriptional regulation of YB-1 gene expression, we examined effects of exogenous 5-and 3-untranslatable region-containing fragments of YB-1 mRNA on its translation and stability in a cell-free system. The addition of the 3 mRNA fragment as well as its subfragment I shut off protein synthesis at the initiation stage without affecting mRNA stability. UV crosslinking revealed four proteins (69, 50, 46, and 44 kDa) that specifically interacted with the 3 mRNA fragment; the inhibitory subfragment I bound two of them, 69-and 50-kDa proteins. We have identified these proteins as PABP (poly(A)-binding protein) (69 kDa) and YB-1 (50 kDa) and demonstrated that titrating out of PABP by poly(A) strongly and specifically inhibits YB-1 mRNA cap ؉ poly(A) ؊ translation in a cell-free system. Thus, PABP is capable of positively affecting YB-1 mRNA translation in a poly(A) tail-independent manner.The evolutionarily conserved family of cold-shock domaincontaining proteins (CSD proteins) 1 is represented in organisms from bacteria to man by multifunctional DNA/RNA-binding proteins (1, 2). In bacteria, some of them known as major cold-shock proteins are responsible for adaptation to growth at low temperatures, and their expression is enormously activated with a temperature decrease (3, 4). In mammalian cells, CSD proteins regulate cell proliferation and differentiation and are involved in cell defense systems (5-11). In the cell nucleus, CSD proteins regulate transcription by interacting with promoters and enhancers of many genes (9, 12-17). They are also involved in DNA replication and repair, as well as in mRNA splicing (5, 18 -20). In the cytoplasm, CSD proteins bind mRNAs, affecting their translation fate (21-28) and extending their lifetime (29).In bacteria, accumulation of major cold-shock proteins at low temperatures was shown to result mainly from strong and selective stabilization of their mRNAs (30, 31). The crucial role of eukaryotic CSD proteins in major cellular events suggests that there is precise regulation of their expression. At present the post-transcriptional control of eukaryotic gene expression is to a large extent attributed to the presence of specific sequences within mRNA 5Ј-and 3Ј-untranslatable regions (UTRs), which serve as targets for binding of certain proteins and complementary RNAs (32, 33). Here, we studied this type of regulation during in vitro synthesis of rabbit p50, a member of the eukaryotic CSD protein family, which is the major protein of reticulocyte mRNPs and is virtually identical to the human Y-box binding protein YB-1. To determine a possible role of YB-1 mRNA UTRs in YB-1 post-transcriptional regulation, we examined effects of exogenous mRNA f...