For many years the main role of RNA, it addition to the housekeeping functions of for example tRNAs and rRNAs, was believed to be a messenger between the genes encoded on the DNA and the functional units of the cell, the proteins This changed drastically with the identification of the first small non-coding RNA, termed microRNA, some 20 years ago This discovery opened the field of regulatory RNAs with no or little protein-coding potential Since then many new classes of regulatory non-coding RNAs, including endogenous small interfering RNAs (endo-siRNAs), PIWI-associated RNAs (piRNAs), and long non-coding RNAs, have been identified and we have made amazing progress in elucidating their expression, biogenesis, mechanisms and mode of action, and function in many, if not all, biological processes In this chapter we provide an introduction about the current knowledge of the main classes of non-coding RNAs, what is know about their biogenesis and mechanism of function

Non-coding RNAs: An Introduction.

Ribonucleic acids (RNA) are generally considered fragile molecules that are readily degraded. However, there is growing documentation of long-term (from days to centuries) RNA persistence in a variety of contexts and tissue types, and as such a number of academic disciplines are beginning to exploit degraded RNA. While the reasons for its survival are not fully understood, there are several plausible mechanisms that would safeguard this molecule against degradation. However, after examining the literature available on the postmortem instability and decay mechanisms of RNA, it has become clear that limited experimental studies and no reviews offer an overview of these mechanisms. Hence in this review we outline molecular reasons for RNA surviving long-term postmortem, and provide specific examples of RNA survival in forensic, archival and archaeological contexts. A better understanding of the mechanisms of RNA decay will be crucial for developing expectations on its long-term survival.

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Long-term RNA persistence in postmortem contexts.

The problem of the existence of a nucleus in the bacterial cell has aroused considerable interest among biologists and has been the subject of numerous investigations. A study of the literature (Knaysi, 1938, 1942a, Delaporte, 19391940, Lewis, 1941) shows that the methods used are various and in some cases ingenious, and that advantage has been taken of developments in other fields of endeavor (Kruis, 1913, Feulgen and Rossenbeck, 1924, Holweck, 1929, Lacassagne, 1929, Piekarski, 1939, Knaysi, 1941). Unfortunately, the net result of this collective effort has been a series of hypotheses ably reclassified by Lewis in his recent review (1941). Confusion has been added by the fact that certain investigators long associated with certain hypotheses have abandoned part or all of their former views. The causes of this confusion have been discussed by Knaysi (1938) who pointed out that they are to be sought, not only in,the small size of the bacterial cell, as is generally believed, but principally in the absence of a single criterion by which an atypical nucleus can be recognized. Consequently, an analysis of the problem led him (1942a) to adopt the following criteria: (a) nucleoprotein nature of a structure, and, (b) behavior of that structure during growth and multiplication, in age and in starvation. Granules which gave a number of tests characteristic of nucleoprotein, which were present in young and old cells and in well-nourished and starved cells, and which did not correspond to any reserve material known to occur in bacteria, were found in Staphylococcus flavo-cyaneus. Moreover those granules were evident during growth of the cell and divided before cell division. Knaysi concluded that those granules represented the cell nucleus.

F W Allen

Papers

The Biochemistry of the Nucleic Acids, Purines, and Pyrimidines