Substitution of the native envelope leader peptide with certain heterologous leaders augmented expression and secretion of envelope, while substitution of the leader peptide of a heterologous protein with the envelope leader peptide slowed ER processing of that protein by delaying folding and maturation of glycosylation. HIV envelope synthesized through heterologous leader peptides in the context of a AbMole 4-Chloropropiophenone complete provirus resulted in decreased envelope incorporation into viral particles and diminished in vitro infectivity. These data suggested that the signal peptide is not merely a passive trafficking signal, but rather an evolving, active modulator of envelope function. The present studies were initiated to examine the function of the signal peptide signature derived computationally by Gnanakaran and colleagues. We hypothesized that a signature located in the leader peptide would manifest itself during envelope synthesis as the leader is cleaved early in the biosynthesis of the glycoprotein. We utilized HIV envelopes from acutely infected individuals to examine the effects of polymorphisms at position 12 on translation of envelope, leader peptide function and viral infectivity. We hypothesized that non-basic residues at position 12 found in chronic envelopes represent evolution away from the transmission genotype. Because of the leader peptide��s primary role in trafficking of newly translated proteins, variation at position 12 of HIV envelope might be expected to manifest itself phenotypically at the level of protein synthesis. Alterations in the rate of endoplasmic reticulum transport of gp160 early during HIV infection may result in higher throughput envelope synthesis, potentially altering the rate of virion production or the protein content of virions produced. Alternatively, the envelope leader��s unusual delayed cleavage and putative role in modulating gp160 interactions with calnexin and other endoplasmic reticulum chaperones suggested a role for leader peptide polymorphisms in modulating envelope structure and glycosylation, potentially impacting on downstream envelope-host interactions. We began our exploration of the effects of the position 12 polymorphism on HIV biology by examining envelope translation. We transiently transfected Jurkat T cells with the 14 transmitted envelope constructs described previously. Forty-eight hours after transfection, we compared expression by Western blot. Comparable transfection efficiencies were confirmed by cotransfection with a GFP expression plasmid. We observed higher levels of steady-state envelope expression by envelopes with a basic residue at position 12 in comparison to those lacking the signature. Using band densitometry to compare relative expression levels, we found that, on AbMole Veratramine average, signature envelope expression was 2.5-fold higher than non-signature envelope expression; the difference in signal intensity between the two groups was highly significant.