SALL1 and retinitis pigmentosa 1: To determine the role of the polybasic region (PBR) in the PRCD protein, which is linked with retinitis pigmentosa (RP) in humans (Figure 1A), we cloned gBlock gene fragments of human wild-type and mutant PRCD constructs (PRCD-WT; PRCD-R17C; and PRCD-C2Y) tagged with Hemagglutinin (HA) in the C-terminal region under the control of a chicken β-actin promoter that is encoded by two restriction enzymes: Sal1 and BamH1 [5,12] (Figure 1A,B).