Point mutations in the FIV-C promoter showing either no effect or abrogating promoter function in an in vitro reporter assay. In an in vitro FIV promoter-β galactosidase reporter system, the promoter of the inoculating virus and the C102A mutated promoter demonstrated strong basal promoter function in (a) feline CRFK and (b) human 293T cells relative to negative controls (no transfection and a promoterless β galactosidase plasmid- no tx and empty, respectively). Cells transfected with a CMV-β galactosidase (CMV) plasmid served as a positive control. Statistical significance is denoted by an asterisk for selected pair wise comparisons (*, p < .05) whereas error bars denote standard deviation. However, cells transfected with the G93A promoter mutant failed to demonstrate a basal promoter function above the negative controls (not significant, NS). The sequence of the promoter in the U3 region of the inoculating FIV-C virus (c) demonstrates multiple cis-acting transcriptional elements (light grey text). The G93A mutation lies within the putative AP-1 binding site whereas C102A is located between binding sites (white arrows).