Veljo Kisand kisand at
Tue Feb 6 17:16:11 EST 1996

Tom Dougherty (Doughert at wrote:

:   An outstanding discussion of the problems and pitfalls of
:  thymine/thymidine metabolism is in Bacteriol. Revs. 34:278-343.  It is still the
:  best discussion of this topic.  The amount of radiolabeled thymidine incorporated
:  is very sensitive to the internal pool level of deoxyribose sugar, and to whether
:  the E. coli strain is a thymidine requiring mutant. 

: Again, I will say, please read the review.  E. coli normally makes dTMP from
: dUMP. This is subsequently phosphorylated to dTDP and finally dTTP.
: Thymidine is NOT in the normal biosynthetic pathway.  It is present only when
: added exogenously.  Check out the diagram on page 464 in "Escherichia
: coli and Salmonella typhimurium, cellular and molecular biology" ASM Press.
: The discussion in the same book on page 466 sums up utilization of 
: thymine and thymidine.   The label on the thymidine is on the base, and not the
: sugar.  This means that radomization of the label does not occur, as the 
: sugar moiety is the part that is broken down and metabolised extensively.     

unfortunately I cannot reach to both references... Anyway I don't understand
how can influence thymidine/tymnine in growth medium growth of E.coli (or
why should be  medium thymidine free)? As you say, E.coli uses normally dUMP
(by the way that is de novo synthesis).So it doesn't
matter at all if there is thymidine in medium or not. Do you know if other
bacteria also prefer to use de novo synthesis instead use of thymidine kinase
for incorporation thymidine into DNA???

Veljo Kisand
ps maybe you can send me reprint and few pages from this book.
tartu univ, inst zoo & hydrobiol, 46 vanemuise st, tartu ee2400, estonia

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