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The retroviral integrase (IN) carries out the integration of a dsDNA copy of the viral genome into the host DNA, an essential step for viral replication. All IN proteins have three general domains, the N-terminal domain (NTD), the catalytic core domain, and the C-terminal domain. The NTD includes an HHCC zinc finger-like motif, which is conserved in all retroviral IN proteins. Two crystal structures of Moloney murine leukemia virus (M-MuLV) IN N-terminal region (NTR) constructs that both include an N-terminal extension domain (NED, residues 1-44) and an HHCC zinc-finger NTD (residues 45-105), in two crystal forms are reported. The structures of IN NTR constructs encoding residues 1-105 (NTR 1-105 ) and 8-105 (NTR 8-105 ) were determined at 2.7 and 2.15 Å resolution, respectively and belong to different space groups. While both crystal forms have similar protomer structures, NTR 1-105 packs as a dimer and NTR 8-105 packs as a tetramer in the asymmetric unit. The structure of the NED consists of three anti-parallel β-strands and an α-helix, similar to the NED of prototype foamy virus (PFV) IN. These three β-strands form an extended β-sheet with another β-strand in the HHCC Zn 2+ binding domain, which is a unique structural feature for the M-MuLV IN. The HHCC Zn 2+ binding domain structure is similar to that in HIV and PFV INs, with variations within the loop regions. Differences between the PFV and MLV IN NEDs localize at regions identified to interact with the PFV LTR and are compared with established biochemical and virological data for M-MuLV. Proteins 2017; 85:647-656. © 2016 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)

HIV load and CD4 cell numbers were measured among 95 HIV infected women during pregnancy in order to determine their value as prognostic markers for transmission of virus from mother to infant. Among the 94 live births, 13 children were infected with HIV, 69 were uninfected and 12 were of unknown infection status. HIV RNA levels, as measured by nucleic acid sequence based amplification, were significantly higher (P < 0.001) in women who transmitted virus than among those who did not transmit and maternal viral load was a stronger predictor of transmission than CD4 cell number. The predicted rate of transmission relative to maternal HIV RNA was 2% at 1,000 copies, 11% at 10,000 copies and 40% at 100,000 copies/ml. Little variation in viral load occurred during pregnancy and there was an association between viral load and prematurity, the mean gestation at delivery decreasing by 1.3 weeks for every 10-fold increase in maternal HIV RNA (P = 0.007). This study demonstrates that a high level of maternal HIV RNA is a risk factor for transmission of virus to the infant and maternal viral load is of more value as a prognostic marker for transmission risk than CD4 cell number. High viral load is also associated with premature delivery. Maternal viral load is therefore a useful marker on which to base management decisions during pregnancy.

The significance of physical breaches of the trophoblastic layer of the placenta in transmission of HIV from mother to infant was evaluated in 17 HIV-infected pregnant women. Samples of peripheral blood were obtained from the women during pregnancy and at delivery, at which time a small piece of placental tissue was obtained from a random site and immediately placed into fixative. Blood samples were obtained from infants at or shortly after birth and thereafter at approximately 3-month intervals, until the age of 18 months, in order to determine their HIV infection status. HIV RNA and p24 antigen were quantified in maternal plasma and CD4 cells enumerated. Paediatric diagnosis was conducted using polymerase chain reaction, virus isolation, detection of p24 antigen, and measurement of class-specific antibodies. Placental damage was quantified and evaluated using transmission electron microscopy. Maternal viral load was low, with a mean RNA copy number of 8,237 per millilitre of plasma (range 230-37,233 copies/ml). Only two women were p24-antigenaemic, and CD4 numbers ranged from 0.09 to 2.8 x 10(9)/l. There was evidence of breaks in the trophoblastic surface to the depth of the basement membrane in all 17 placentas, and perivillous fibrinoid deposits were also observed to a varying degree in all samples. However, none of the 13 infants available for follow-up had evidence of infection with HIV. Superficial damage to the trophoblastic surface of the placenta, with exposure of the basement membrane and potential exposure of CD4-expressing cells, does not appear to be a significant factor in the transmission of HIV from mother to infant during pregnancy.