Stem-loop binding protein, the protein that binds the 3' end of histone mRNA, is cell cycle regulated by both translational and posttranslational mechanisms.
The expression of the replication-dependent histone mRNAs is tightly regulated during the cell cycle. As cells progress from G(1) to S phase, histone mRNA levels increase 35-fold, and they decrease again during G(2) phase. Replication-dependent histone mRNAs are the only metazoan mRNAs that lack polyadenylated tails, ending instead in a conserved stem-loop. Much of the cell cycle regulation is posttranscriptional and is mediated by the 3' stem-loop. A 31-kDa stem-loop binding protein (SLBP) binds the 3' end of histone mRNA. The SLBP is necessary for pre-mRNA processing and accompanies the histone mRNA to the cytoplasm, where it is a component of the histone messenger RNP. We used synchronous CHO cells selected by mitotic shakeoff and HeLa cells synchronized at the G(1)/S or the M/G(1) boundary to study the regulation of SLBP during the cell cycle. In each system the amount of SLBP is regulated during the cell cycle, increasing 10- to 20-fold in the late G(1) and then decreasing in the S/G(2) border. SLBP mRNA levels are constant during the cell cycle. SLBP is regulated at the level of translation as cells progress from G(1) to S phase, and the protein is rapidly degraded as they progress into G(2). Regulation of SLBP may account for the posttranscriptional component of the cell cycle regulation of histone mRNA.
Whitfield
M L
ML
Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, USA.
Zheng
L X
LX
Baldwin
A
A
Ohta
T
T
Hurt
M M
MM
Marzluff
W F
WF
D000818:Animals; D016466:CHO Cells; D002453:Cell Cycle; D006224:Cricetinae; D004261:DNA Replication; D006657:Histones / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D006657:Histones; D009687:Nuclear Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins