T--------------------------------------Tail

Fig. 3. Schematic picture of a macromolecule in the adsorbent pore. S sequence, L loop, B bridge, T tail of macromolecule...

Fig. 6.4. The possible outcomes of tossing a coin 4 times. H = heads, T=tails.

Mature mRNA transcripts (sense strand) from eukaryotic cells can be purified and then reverse transcribed, with the assistance of a reverse transcriptase enzyme (from Moloney murine leukemia virus, MMLV), into complementary DNAs (cDNAs) that will anneal with the mRNA transcripts by Watson-Crick base pairing to give anti-parallel DNA/RNA duplexes or double helices. The poly(A) tail in each mature mRNA transcript is actually a usefiil handle for each reverse transcriptase reaction. Thereafter, DNA/RNA duplexes must be broken down with the assistance ofRNAse enzymes (specific for the hydrolysis of RNA phospho diester links) and a sense strand of DNA constructed instead on each cDNA single strand so that equivalent, more stable antiparallel DNA/DNA duplexes are generated instead, with the assistance of a DNA polymerase enzyme. In this instance, the poly(T) tail in each cDNA molecule turns out to be important for the DNA polymerase reaction ... 

The presence of the poly-A tail has been very fortuitous for researchers. By designing an affinity chromatography column (Chapters 5 and 13) with a poly-T tail (or poly[d(T)] tail), the isolation of mRNA from a cell lysate... 

The cDNA prepared from mRNA would have a long poly(T) tail, unlike genomic DNA. Remember that the poly(A) tail is added to the 3 end of mammalian mRNA and that there is no counterpart on DNA. A second striking difference would be that the cDNA would contain no intervening sequences (introns) and would therefore be much shorter... 

T = tail end load, lb Tb = bolt pretension load, lbs T, = tangential force, lb wi = fillet weld size, shell to re-pad W2 = fillet weld size, re-pad to shell W3 = fillet weld size, pad eye to lug VV4 = fillet weld size, base plate to skirt W5 = uniform load on vessel, IbAn. 

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