PCR validations of each cDNA size fraction obtained from soil samples PL, BB and UP. All three cDNA size fractions from each soil were tested for cross-contaminations by PCR amplification of conserved genes of different length. (A) Approximate size of coding sequences of each of the four tested genes and positions of the PCR primers. (B) Gel electrophoresis of the PCR products showing perfect correlation between sized cDNA fraction and detection of a PCR product from genes whose expected size is included in the corresponding fraction size range. In fraction C, only, elongation factor 1-alpha and beta-tubulin genes were amplified while in fraction B, only ribosomal protein S3 and peptide methionine sulphoxide reductase genes were detected whereas none of theses genes was amplified from fraction A.