tokens: To further map the p53 mRNA transcribed in these cells , series of RT - PCR tests were performed using the forward primer , F2 ( exon 8 position 1008th according to GenBank accession no . K03199 ) , matched with different reverse primers , R3 ( at the junction of exon 8 / 9 , nt position 1124 ) , R4 , R5 ( in exon 9 at positions 1154 and 1184 , respectively ) , and R6 ( in exon 10 , at position 1230 ) .