Several studies report the observation that RNA degradation does not correlate with PMI in tissue frozen 36 hours or more after death (Barton, Pearson, Najlerahim, & Harrison, 1993; Heinrich, Matt, Lutz-Bonengel, & Schmidt, 2007). At the same time, there is evidence of the selective reduction in mRNA at PMIs of 48 hrs or more (Catts, et al., 2005). It was shown that increasing PMI is associated with the increase of RNA degradation (accordingly the index 28S/18S ribosomal RNA ratio). By the PMI of 48 hrs, about 12% of mRNAs show more than a two-fold decrease in abundance; transcription factors with a specific structure (carrying the AUUUA polynucleotide motif in the 3′UTR–3′ untranslated region of RNA, the, sequences on the 3′ end of an mRNA that are not translated into protein) prevail among RNAs that are susceptible to PMI-related degradation. This finding suggests that PMI-related RNA degradation might affect the spectrum of mRNA transcripts in postmortem tissue that ultimately might lead to the selective elimination of certain populations of RNA-molecules and significantly impact the original transcriptional profile in studied tissue (Catts, et al., 2005).
