Specific combinations of SR proteins associate with single pre-messenger RNAs in vivo and contribute different functions.
Serine/arginine-rich (SR) proteins are required for messenger RNA (mRNA) processing, export, surveillance, and translation. We show that in Chironomus tentans, nascent transcripts associate with multiple types of SR proteins in specific combinations. Alternative splicing factor (ASF)/SF2, SC35, 9G8, and hrp45/SRp55 are all present in Balbiani ring (BR) pre-messenger ribonucleoproteins (mRNPs) preferentially when introns appear in the pre-mRNA and when cotranscriptional splicing takes place. However, hrp45/SRp55 is distributed differently in the pre-mRNPs along the gene compared with ASF/SF2, SC35, and 9G8, suggesting functional differences. All four SR proteins are associated with the BR mRNPs during export to the cytoplasm. Interference with SC35 indicates that SC35 is important for the coordination of splicing, transcription, and 3' end processing and also for nucleocytoplasmic export. ASF/SF2 is associated with polyribosomes, whereas SC35, 9G8, and hrp45/SRp55 cosediment with monoribosomes. Thus, individual endogenous pre-mRNPs/mRNPs bind multiple types of SR proteins during transcription, and these SR proteins accompany the mRNA and play different roles during the gene expression pathway in vivo.
Björk
Petra
P
Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden.
Jin
ShaoBo
S
Zhao
Jian
J
Singh
Om Prakash
OP
Persson
Jan-Olov
JO
Hellman
Ulf
U
Wieslander
Lars
L
D000818:Animals; D002460:Cell Line; D002683:Chironomidae / Q000378:metabolism*; D005786:Gene Expression Regulation; D019476:Insect Proteins / Q000378:metabolism*; D007438:Introns; D014176:Protein Biosynthesis; D012322:RNA Precursors / Q000378:metabolism*; D034443:RNA Transport; D012261:Ribonucleoproteins / Q000378:metabolism; D028961:beta Karyopherins / Q000378:metabolism*
D019476:Insect Proteins; D012322:RNA Precursors; D012261:Ribonucleoproteins; D028961:beta Karyopherins; C119888:transportin SR