cDNA sequences of chicken nucleolin/C23 and NO38/B23, two major nucleolar proteins.

Nucleolin and NO38 are abundant nucleolar proteins implicated in the transcription and processing of ribosomal RNA, and in the packaging and transport of ribosomal proteins or preribosomal particles (for references see 1-5). cDNAs encoding the chicken homologs of these proteins were cloned (by lmmunoscreening; 6) from Xgtll cDNA expression libraries prepared from poly(A)+ RNA of 10 day old chicken embryos (7)-DNA from recombinant phages was prepared using lambdasorb (Promega), and preliminary sequence determination was carried out directly on X phages, using Klenow polymerase and primers obtained from Biolabs. In the case of NO38, the complete coding information was contained within a single 1.1 kb £coRI fragment, which was subcloned into the Ec691 site of the pGEM-3Zf(vector or (Promega). The nucleolin insert contained four internal £coRI sites, and, therefore, a 2.5 kb fragment was excised from the recombinant Xgtl 1 phage using DraR. The resulting fragment was filled up with Klenow polymerase and blunt-end ligated into the Smal site of pGEM-3Zf (Nested ted deletion templates for sequence analysis were then generated by exonuclease HI digestion (8), using Xbal and Sphl for plasmid linearization. Sequencing of double-stranded plasmid DNA (9) was earned out (in both orientations) by the dideoxy method (10) using T7 polymerase (Sequenase, United States Biochemicals).