Analysis of human/hamster Xpr1 chimeras for receptor function. The predicted transmembrane domain structure of Xpr1 is shown at top and a corresponding block diagram is shown just below with the extracellular loops (ECL) shown in grey. A series of chimeras were constructed by exchange of the indicated fragments of hXpr1 and haXpr1. Restriction enzyme sites used in construction of the Xpr1 chimeras are shown above the block diagram. Chimeric receptors were subcloned into a retroviral expression vector and were transfected into CHO cells. The cells were then grown in medium containing G418 to select for expression of the Neo gene also carried by the expression plasmid. Cells were then exposed to LAPSN vectors bearing either the AKR6 or the 1E Env and the apparent titers of the vectors were determined. Results are means of at least two independent experiments with triplicate determinations in each experiment.