The strategy used for the generation of OR complete 5′-end cDNA sequences. (A) Truncated mRNAs were dephosphorylated using calf intestine phosphatase (CIP) so that they cannot participate in subsequent ligation reactions. The RNA was then treated with tobacco acid pyrophosphatase (TAP) to remove the 5′-cap structure (represented by black balls) from intact full-length mRNA, and the GeneRacer RNA oligo-nucleotide was ligated to the decapped mRNA. Reverse transcription was performed using oligo(dT) primers. To obtain 5′-ends, PCR was done using the GeneRacer 5′-primer and a degenerate primer directed toward conserved OR regions (P8 or P27). Nested PCR was then done using the GeneRacer 5′ nested primer and another OR degenerate reverse primer (P27 or P26R). (B) Schematic representation of an OR coding region showing the seven transmembrane regions (I–VII) and the regions matched by the degenerate primers used in this study. (C) 1.5% agarose gel showing the PCR products obtained using different combinations of primers. (Lane 1) Negative control for reaction in lane 2 (no DNA added); (lane 2) GeneRacer 5′-primer and P27; (lane 3) GeneRacer 5′ nested primer and P26R; (lane 4) negative control for reaction in lane 5 (no DNA added); (lane 5) GeneRacer 5′-primer and P8; (lane 6) GeneRacer 5′ nested primer and P27. (M) Molecular weights are given in kilobases.