Abstract
Human APOBEC3G (hA3G) is a host factor that defends against HIV-1 as well as other exogenous retroviruses and endogenous retroelements. To this end, hA3G is restricted to the cytoplasm of T lymphocytes where it interacts with viral RNA and proteins to assemble with viral particles causing a post-entry block during reverse transcription. hA3G also exhibits a mechanism to inhibit the reverse transcription of retroelements by RNA binding and sequestration into mRNA processing centers in the cytoplasm. We have determined that the molecular basis for this specialized property of hA3G is a novel cytoplasmic retention signal (CRS) that is necessary and sufficient to restrict wild-type hA3G and chimeric constructs to the cytoplasm. The CRS resides within amino acids 113-128 and is embedded within a basic flanking sequence and does not require RNA binding to retain hA3G in the cytoplasm. Paralogs of hA3G that have nuclear or cytoplasmic distributions differ from hA3G within the region encompassing the CRS motif with respect to charge and amino acid composition. We propose that the CRS enables hA3G to interact with cytoplasmic factors, and thereby enables hA3G to serve in host cell defense by restricting an antiviral sentinel to the cytoplasm. The CRS lies in a region involved in both Gag and Vif interactions; therefore, identification of this motif has important implications for the design of therapeutics that target HIV-1 while maintaining antiviral and cellular functions.
Highlights
The cytoplasmic retention signal (CRS) Is within the N-terminal Half of human APOBEC3G (hA3G)—Previously, we utilized indirect immunostaining of fixed HeLa cells to determine that hA3G was actively retained in the cytoplasm even when a strong nuclear localization signal (NLS) from SV40 was added onto the protein (48)
We have tested the hypothesis that hA3G is actively retained in the cytoplasm through its own cytoplasmic retention signal (CRS) by evaluating the subcellular distribution of hA3G domains expressed as EGFP and NLS-EGFP chimeric reporters
We demonstrated that the sequence KVTLTIFVARLYYFWD within the N-terminal portion of hA3G is a novel CRS that restricts hA3G to the cytoplasm and is capable of autonomous function within the context of chimeric reporters
Summary
Constructs lacking this region (amino acids 1– 60, 1–111) distributed to both the cytoplasm and nucleus (Fig. 4, D and E), similar to that observed with EGFP alone (Fig. 1A) suggesting the loss of CRS function. The data corroborate our findings with NLS-EGFP chimeric deletion constructs of hA3G suggesting that the region including the predicted 4 is essential for cytoplasmic retention.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
