The negative factor (nef) of human immunodeficiency virus (HIV) type 1 acts to down-regulate virus replication.

The c-sis gene encodes the B polypeptide chain of platelet-derived growth factor (PDGF), and is expressed in a number of normal and pathological conditions. In order to study the control of synthesis of the human c-sis product, we have initiated a study of two regions of this genetic locus which regulate transcription and translation. A clone of the 5' portion of the gene was obtained which included 1361 nucleotides upstream of the RNA initiation site. Transcriptional promoter activity of this region was demonstrated in normal and transformed cells using a plasmid with the sequences upstream of the c-sis RNA initiation site fused to an indicator gene, chloramphenicol acetyl transferase. Experiments were also performed to identify other possible regulatory regions of the c-sis gene. These data demonstrated that a portion of the c-sis first exon encoding the 5' untranslated region of the c-sis mRNA inhibited synthesis of the PDGF B product in vitro. These results define regions of the c-sis gene whose activity may be important in the regulation of transcription and translation under normal conditions and in the pathogenesis several human diseases.

Human immunodeficiency virus type 1 isolates were obtained over a 3-year period from blood, brain, and lung of three patients in a clustered infectious outbreak. This included a blood donor who was initially asymptomatic but subsequently developed AIDS-related complex and two neonatal transfusion recipients who developed AIDS. Isolates from brain and lung replicated to >30-fold higher levels in primary monocyte cultures than did those from blood; no growth differences on primary lymphocytes were observed. Thirteen clones were obtained from seven isolates, and env sequences were determined. The predicted amino acid sequences among these clones differed by only 0.01% but differed by 15-27% when compared to previously sequenced iates from other

SUMMARYSeveral retroviruses encode trans-acting factors which activate gene expression directed by long terminal repeat (LTR) sequences and play a role in the positive feedback regulation of virus replication. We have examined two Mason-Pfizer monkey virus (MPMV) strains for their ability to produce and respond to such factors. Plasmids with the LTR of either MPMV or type D retrovirus/New England (D/NE) were fused to the bacterial chloramphenicol acetyltransferase (CAT) gene. Introduction of these plasmids into several different human cell lines gave rise to significant CAT activity, demonstrating the strong transcriptional promoter activity of these LTRs. However, little or no increase in CAT activity was found upon transfection of these plasmids into MPMV-or D/NE-infected cell lines as compared with uninfected cell lines. Furthermore, CAT activity was not enhanced in uninfected cells by cotransfecting either a functional MPMV DNA clone, a plasmid expressing the human Tlymphotropic retrovirus trans-activator genes, tat-1 or tat-3. These data show that the property of trans-activation of LTR-mediated gene expression is a function in the replication of only certain retroviruses.