NAB2: a yeast nuclear polyadenylated RNA-binding protein essential for cell viability.
A variety of nuclear ribonucleoproteins are believed to associate directly with nascent RNA polymerase II transcripts and remain associated during subsequent nuclear RNA processing reactions, including pre-mRNA polyadenylation and splicing as well as nucleocytoplasmic mRNA transport. To investigate the functions of these proteins by using a combined biochemical and genetic approach, we have isolated nuclear polyadenylated RNA-binding (NAB) proteins from Saccharomyces cerevisiae. Living yeast cells were irradiated with UV light to covalently cross-link proteins intimately associated with RNA in vivo. Polyadenylated RNAs were then selectively purified, and the covalent RNA-protein complexes were used to elicit antibodies in mice. Both monoclonal and polyclonal antibodies which detect a variety of NAB proteins were prepared. Here we characterize one of these proteins, NAB2. NAB2 is one of the major proteins associated with nuclear polyadenylated RNA in vivo, as detected by UV light-induced cross-linking. Cellular immunofluorescence, using both monoclonal and polyclonal antibodies, demonstrates that the NAB2 protein is localized within the nucleus. The deduced primary structure of NAB2 indicates that it is composed of at least two distinct types of RNA-binding motifs: (i) an RGG box recently described in a variety of heterogeneous nuclear RNA-, pre-rRNA-, mRNA-, and small nucleolar RNA-binding proteins and (ii) CCCH motif repeats related to the zinc-binding motifs of the largest subunit of RNA polymerases I, II, and III. In vitro RNA homopolymer/single-stranded DNA binding studies indicate that although both the RGG box and CCCH motifs bind poly(G), poly(U), and single-stranded DNA, the CCCH motifs also bind to poly(A). NAB2 is located on chromosome VII within a cluster of ribonucleoprotein genes, and its expression is essential for cell growth.
Anderson
J T
JT
Department of Immunology and Medical Microbiology, College of Medicine, University of Florida, Gainesville 32610-0266.
Wilson
S M
SM
Datar
K V
KV
Swanson
M S
MS
D000595:Amino Acid Sequence; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D015825:Chromosomes, Fungal; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D005656:Fungal Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D029543:Nucleocytoplasmic Transport Proteins; D009838:Oligodeoxyribonucleotides; D010957:Plasmids; D012331:RNA, Fungal / Q000235:genetics / Q000302:isolation & purification; D012333:RNA, Messenger / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D015183:Restriction Mapping; D012261:Ribonucleoproteins / Q000378:metabolism / Q000528:radiation effects; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D014466:Ultraviolet Rays
D004271:DNA, Fungal; D005656:Fungal Proteins; C080773:NAB2 protein, S cerevisiae; D029543:Nucleocytoplasmic Transport Proteins; D009838:Oligodeoxyribonucleotides; D012331:RNA, Fungal; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D012261:Ribonucleoproteins; D029701:Saccharomyces cerevisiae Proteins