CNBP: an RNA binding protein differentially expressed during development.

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

Villa Carlos Paz, Cordoba, Argentina.

Congreso; XXXVIII Reunión anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular.; 2002

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular.

Ribosomal protein mRNAs (rp-mRNAs) translation is regulated during early development according to the needs of translational machinery of embryo cells. The cellular nucleic acid binding protein (CNBP) specifically binds in vitro the 5’UTR of rp-mRNAs, possibly inhibiting their translation. The biological role of CNBP has not been addressed, but its structure and expression pattern show several items of interest. Bufo arenarum CNBP is a 19.4 kDa protein containing seven CCHC zinc finger motifs, an RGG box and six putative phosphorylation sites. RNA-band-shift assays were performed so as to analyze the ability of embryo extracts and recombinant-expressed CNBP (GST-CNBP) to bind a ribo-probe containing a Xenopus rp-mRNA’s 5’UTR. Egg and blastula extracts were able to bind per se the ribo-probe with high affinity, but gastrula extracts did not show any binding activity, indicating that CNBP binding capacity decreases through early development, mainly after mid-blastula transition. GST-CNBP was not capable of binding the ribo-probe by its own, whereas when co-incubated with gastrula extracts it was able to bind the probe. Band-shift assays performed with single-stranded oligonucleotide-probe confirmed these observations. These results suggest that CNBP may need some cellular component to bind its RNA target and might be involved in its function as nucleic acid binding protein since mid-blastula stage, when the rp-mRNA are transcribed from zigotic nuclei but silenced and not translated until needed, later in development.