CARF is a novel protein that cooperates with mouse p19ARF (human p14ARF) in activating p53

The INK4a locus on chromosome 9p21 encodes two structurally distinct tumor suppressor proteins, p16(INK4a) and the alternative reading frame protein, ARF (p19(ARF) in mouse and p14(ARF) in human). Each of these proteins has a role in senescence of primary cells and activates pathways for cell cycle control and tumor suppression. The current prevailing model proposes that p19(ARF) activates p53 function by antagonizing its degradation by MDM2. It was, however, recently shown that stabilization of p53 by p14(ARF) occurs independent of the relocalization of MDM2 to the nucleolus. We have identified a novel collaborator of ARF, CARF. It co-localizes and interacts with ARF in the nucleolus. We demonstrate that CARF is co-regulated with ARF, cooperates with it in activating p53, and thus acts as a novel component of the ARF-p53-p21 pathway.     

LexA analog (dra0074) is a regulatory protein that is irrelevant to recA induction

The protein DRA0074 is suggested to be another LexA in Deinococcus radiodurans, having similar motifs and RecA-mediated cleavage activity to D. radiodurans LexA (dra0344). However, its function has not been studied. We disrupted the gene dra0074 and measured its effect on RecA induction using fusion translation, immunoblot, and proteomic analysis. Results showed that the product of gene dra0074 is not involved in RecA induction, but is a regulator of other metabolisms in D. radiodurans.     

4-Hydroxynonenal induces a DNA-binding protein similar to the heat-shock factor.

By using a gel mobility assay, we have shown that treatment of HeLa cells with 4-hydroxynonenal, a major product of the peroxidation of membrane lipids and an inducer of heat-shock proteins, has the same effect as heat shock in causing the appearance of a protein which binds to the sequence of DNA specific for the induction of heat-shock genes. Lipoperoxidation and heat exposure seem to share a common mechanism of specific gene activation.     

Human immunodeficiency virus vpr product is a virion-associated regulatory protein.

The vpr product of the human immunodeficiency virus type 1 (HIV-1) acts in trans to accelerate virus replication and cytopathic effect in T cells. Here it is shown that the HIV-1 viral particle contains multiple copies of the vpr protein. The vpr product is the first regulatory protein of HIV-1 to be found in the virus particle. This observation raises the possibility that vpr acts to facilitate the early steps of infection before de novo viral protein synthesis occurs.     

E. coli ribosomal protein L4 is a feedback regulatory protein

We studied the synthesis of ribosomal proteins encoded by the S10 operon, an eleven gene operon from the str-spc region of the E. coli chromosome, using a λfus3 DNA-directed, in vitro protein synthesizing system. Addition of ribosomal protein L4 (1 μM) to in vitro protein synthesis reactions caused selective inhibition of synthesis of the promoter-proximal proteins of the S10 operon, S10, L3, L4, L23 and possibly L2. Proteins of the S10 operon other than L4 did not cause selective inhibition of protein synthesis. Autoregulatory ribosomal proteins previously identified from other operons, L1, S4 and S8, did not inhibit protein synthesis from the S10 operon; nor did L4 cause significant inhibition of protein synthesis from operons other than the S10 operon. As with L1, S4 and S8, L4 inhibits gene expression at the level of translation.     

Human plasma retinol-binding protein (RBP4) is also a fatty acid-binding protein

RBP4 (plasma retinol-binding protein) is the 21?kDa transporter of all-trans retinol that circulates in plasma as a moderately tight 1:1 molar complex of the vitamin with the protein. RBP4 is primarily synthesized in the liver but is also produced by adipose tissue and circulates bound to a larger protein, transthyretin, TTR, that serves to increase its molecular mass and thus avoid its elimination by glomerular filtration.This paper reports the high resolution three-dimensional structures of human RBP4 naturally lacking bound retinol purified from plasma, urine and amniotic fluid. In all these crystals we found a fatty acid molecule bound in the hydrophobic ligand-binding site, a result confirmed by mass spectrometry measurements.In addition we also report the 1.5?Å resolution structures of human holo-RBP4 and of the protein saturated with palmitic and lauric acid and discuss the interaction of the fatty acids and retinol with the protein.     

Human claspin is a ring-shaped DNA-binding protein with high affinity to branched DNA structures

Claspin is an essential protein for the ATR-dependent activation of the DNA replication checkpoint response in Xenopus and human cells. Here we describe the purification and characterization of human Claspin. The protein has a ring-like structure and binds with high affinity to branched DNA molecules. These findings suggest that Claspin may be a component of the replication ensemble and plays a role in the replication checkpoint by directly associating with replication forks and with the various branched DNA structures likely to form at stalled replication forks because of DNA damage.     

Evidence that eukaryotic initiation factor (eIF) 2 is a cap-binding protein that stimulates cap recognition by eIF-4B and eIF-4F

We studied the mRNA-binding properties of eukaryotic initiation factor (eIF) 2. This Met-tRNA-binding factor interacts with the cap structure of reoviral mRNA in an ATP-independent manner. Both the beta- and gamma-subunit of eIF-2 are involved in the UV-induced cross-linking of eIF-2 to the cap. The interaction of eIF-2 with a messenger is sensitive to the cap analogue 7-methyl-guanosine 5'-triphosphate as measured by cross-linking and by mRNA retention on nitrocellulose filters. The cap-binding property of eIF-2 does not conflict with the current mRNA-binding model of initiation factors eIF-4A, -4B, and -4F: cross-linking of eIF-4E and of eIF-4B is stimulated by eIF-2. The eIF-2-mediated increase of eIF-4E interaction results in a decrease of the cross-linking of the beta- and gamma-subunits of eIF-2. The presence of GTP in the cross-linking assay interferes with the interaction of eIF-2 with the cap structure but does not inhibit the eIF-2 stimulated eIF-4E and -4B cross-linking. These observations indicate a role for eIF-2 in the mRNA recognition.