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Research Article |
1 From the Department of Biochemistry and Biophysics, University of Rochester
School of Medicine and Dentistry, Rochester, New York 14642, USA
3 From the Department of Pathology, University of Rochester School of Medicine
and Dentistry, Rochester, New York 14642, USA
2 From the Department of the Environmental Health Sciences, University of
Rochester School of Medicine and Dentistry, Rochester, New York 14642,
USA
4 From the Department of Cancer Centers, University of Rochester School of
Medicine and Dentistry, Rochester, New York 14642, USA
* Present address: Prairie View A & M University, Prairie View, TX 77446,
USA
Author for correspondence (e-mail:
harold_smith{at}urmc.rochester.edu
)
Accepted 4 December 2001
Apolipoprotein B mRNA cytidine to uridine editing requires the assembly of a multiprotein editosome comprised minimally of the catalytic subunit, apolipoprotein B mRNA editing catalytic subunit 1 (APOBEC-1), and an RNA-binding protein, APOBEC-1 complementation factor (ACF). A rat homolog has been cloned with 93.5% identity to human ACF (huACF). Peptide-specific antibodies prepared against huACF immunoprecipitated a rat protein of similar mass as huACF bound to apolipoprotein B (apoB) RNA in UV cross-linking reactions, thereby providing evidence that the p66, mooring sequence-selective, RNA-binding protein identified previously in rat liver by UV cross-linking and implicated in editosome assembly is a functional homolog of huACF. The rat protein (p66/ACF) was distributed in both the nucleus and cytoplasm of rat primary hepatocytes. Within a thin section, a significant amount of total cellular p66/ACF was cytoplasmic, with a concentration at the outer surface of the endoplasmic reticulum. Native APOBEC-1 co-fractionated with p66/ACF in the cytoplasm as 60S complexes. In the nucleus, the biological site of apoB mRNA editing, native p66/ACF, was localized to heterochromatin and fractionated with APOBEC-1 as 27S editosomes. When apoB mRNA editing was stimulated in rat primary hepatocytes with ethanol or insulin, the abundance of p66/ACF in the nucleus markedly increased. It is proposed that the heterogeneity in size of complexes containing editing factors is functionally significant and reflects functionally engaged editosomes in the nucleus and an inactive cytoplasmic pool of factors.
Key words: APOBEC-1, Editing, Ethanol, Insulin, Nucleus
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