TABLE 1.
Viral and Cellular Factors Affecting Retroviral Gene Expression
| Virus | HIV | HTLV | MMTV | MPMV | MLV | RSV |
|---|---|---|---|---|---|---|
| Simple or complex virus | Complex | Complex | Complex | Simple | Simple | Simple |
| Transcription | ||||||
| Viral effector | Tat | Tax | None | None | None | None |
| cis-acting RNA sequence | TAR | TAR | None | None | None | None |
| Splicing | ||||||
| Alternative splicing | Yes | Yes | Yes | No | No | Yes |
| Protein-coding mRNAs1 | 7 | 4 | 62 | 2 | 2 | 3 |
| Nuclear export | ||||||
| Viral effector | Rev | Rex | Rem | None | None | None |
| cis-acting element | RRE | RexRE | RemRE | CTE | Unknown | DR |
| Cellular factors | CRM1 | CRM1 | CRM1 | Tap | Unknown | Tap |
| NPC elements | DDX3 | Unknown | Unknown | Unknown | Unknown | Dbp5 |
| Translation | ||||||
| Frame shift sites | One | Two | Two | Two | None3 | One |
| 5′ UTR PCE | Present | Present | Unknown | Present | Unknown | Unknown |
CTE, constitutive transport element; HIV, human immunodeficiency virus; HTLV, human T-lymphotropic virus; MMTV, mouse mammary tumor virus; MPMV, Mason-Pfizer monkey virus; MLV, murine leukemia virus; RSV, Rous sarcoma virus; RRE, Rev Response Element; RexRE, Rex-responsive element; TAR, trans-activating region.
1
Includes only the abundantly expressed mRNAs; minor splice variants are omitted.
2
Includes the three distinct sag mRNAs, which encode the viral superantigens.
3
MLV read through across the gag-pol junction occurs via termination codon suppression using a glutamine tRNA.