TI - Identification of a polymorphism for allele -specific transcript analysis . AB - DNA and RNA were extracted , purified and used as a template for sequencing and searching for single nucleotide polymorphisms ( SNP ) between the Bos taurus and Bos indicus subspecies . In comparison to the Bos taurus published sequence ( GeneBank : AF101040 ) , we detected an adenine (A) to guanine (G) transition in Bos indicus DNA located in exon 2 ( position 151 ) of the SNURF-SNRPN upstream reading frame protein [21] , the 71 amino acid protein SNURF that encompasses exons 1-3 ( Figure 1 ) . Interestingly , this Bos indicus-specific missence mutation leads to the substitution of an asparagine to a serine in codon 50 , a position within a PHOSphorylation site for casein kinase II ( CK2 ) . In contrast to the widespread conservation of SNURF , Bos taurus SNURF differed at this position whereas our findings show that the Bos indicus SNURF CK2 site is homologous to other mammals , including humans [21] . Genomic DNA samples were obtained from Bos taurus ( maternal ) , Bos indicus ( paternal ) and crossbred tissues ( Bos indicus versus Bos taurus ) . Whereas the G and A where consistently found in Bos indicus and Bos taurus samples , an overlap of G/A nucleotides was detected in the sequence chromatograms of F1 genomic DNA confirming the use of interspecies F1 crosses for allele -specific gene expression analysis . Between 15 and 20 clones were selected and sequenced for allele expression analysis of each sample .