The six remaining genes, tat, rev, nef, vif, vpr, and vpu (or vpx in the case of HIV-2), are regulatory genes for proteins that control the ability of HIV to infect cells, produce new copies of virus (replicate), or cause disease.The two tat proteins (p16 and p14) are transcriptional transactivators for the LTR promoter acting by binding the TAR RNA element. The TAR may also be processed into microRNAs that regulate the apoptosis genes ERCC1 and IER3. The rev protein (p19) is involved in shuttling RNAs from the nucleus and the cytoplasm by binding to the RRE RNA element. The vif protein (p23) prevents the action of APOBEC3G (a cellular protein that deaminates cytidine to uridine in the single-stranded viral DNA and/or interferes with reverse transcription). The vpr protein (p14) arrests cell division at G2/M. The nef protein (p27) down-regulates CD4 (the major viral receptor), as well as the MHC class I and class II molecules.Nef also interacts with SH3 domains. The vpu protein (p16) influences the release of new virus particles from infected cells. The ends of each strand of HIV RNA contain an RNA sequence called a long terminal repeat (LTR). Regions in the LTR act as switches to control production of new viruses and can be triggered by proteins from either HIV or the host cell. The Psi element is involved in viral genome packaging and recognized by gag and rev proteins. The SLIP element (TTTTTT) is involved in the frameshift in the gag-pol reading frame required to make functional pol.
Recurrent miscarriage is three or more consecutive pregnancy losses. In contrast, infertility is the inability to conceive. In many cases the cause of RPL is unknown. After three or more losses, a thorough evaluation is recommended by American Society of Reproductive Medicine. About 1% of couples trying to have children are affected by recurrent miscarriage. Causes
There are various causes for recurrent miscarriage, and some can be treated. Some couples never have a cause identified, often after extensive investigations. About 50–75% of cases of recurrent miscarriage are unexplained. Chromosomal disorders
A balanced translocation or Robertsonian translocation in one of the partners leads to unviable fetuses that are miscarried. This explains why a karyogram is often performed in both partners if a woman has experienced repeated miscarriages.Aneuploidy may be a cause of a random spontaneous as well as recurrent pregnancy loss. Aneuploidy is more common with advanced reproductive age reflecting decreased germ cell quality.Larger chromosomal disorders are generally detected on karyotype. In couples where a miscarried embryo has an abnormal karyotype, 76% of subsequent miscarried embryos have shown abnormal karyotypes as well. On the other hand, this group of couples have a better long-term live birth rate than those where miscarried embryos have normal karyotype. Lifestyle factors
While lifestyle factors have been associated with increased risk for miscarriage in general, and are usually not listed as specific causes for RPL, every effort should be made to address these issues  in patients with RPL. Of specific concern are chronic exposures to toxins including smoking, alcohol, and drugs.