Cellular nucleic acid binding protein binds G-rich single-stranded nucleic acids and may function as a nucleic acid chaperone through its Arg-Gly rich box motif.

ARMAS, P.; NASIF, S.; CALCATERRA, N.B.

Bariloche, Neuquen, Argentina.

Workshop; Combined ICGEB and EURASNET meetings on "Gene Expression and RNA processing" and "Cell Biology, Signaling and Alternative Splicing".; 2007

ICGEB and EURASNET

Cellular nucleic acid binding protein (CNBP) is a small single-stranded nucleic acid binding protein made of seven CCHC Zn knuckles and an Arg-Gly rich RGG box. CNBP is strikingly conserved among vertebrates and was reported to play broad-spectrum functions in eukaryotic cells. It has been implicated in vertebrate embryogenesis, being required for rostral head development. However, neither its cellular function nor its molecular mechanisms of action were completely elucidated yet. In order to gain further insights into the CNBP biochemical and molecular features we studied Bufo arenarum CNBP (bCNBP) binding to single-stranded nucleic acid probes representing the main reported CNBP putative targets. bCNBP is able to bind RNA and single-stranded DNA (ssDNA) probes in vitro, binding RNA as a preformed dimer whereas both monomer and dimer are able to bind to ssDNA. A systematic analysis of variant probes shows that the preferred bCNBP targets contain unpaired guanosine-rich stretches compatible with the formation of G-quadruplex, a non-conventional nucleic acid structure involved in gene expression regulation. Besides, we show that bCNBP presents a highly disordered predicted structure and promotes the annealing and melting of nucleic acids in vitro. These features are typical of proteins that function as nucleic acid chaperones. Site-directed and deletion CNBP mutants showed that CNBP RNA binding and nucleic acid chaperone activities depend mainly on the RGG box. Considering that a natural proteolytic CNBP form lacks the RGG box, proteolysis could be a specific strategy for CNBP biochemical activity regulation. Based on these data, we propose that CNBP may function as a nucleic acid chaperone through binding, remodeling, and stabilizing nucleic acids secondary structures. This novel CNBP biochemical activity broadens the field of study about its biological function and may be the basis to understand the diverse ways in which CNBP controls gene expression.