Antisense and sensibilities
malexeyev at biost1.thi.tmc.edu
Thu Jan 4 20:59:28 EST 1996
In article <Pine.3.89.9601041725.C19223-0100000 at mistral.ERE.UMontreal.CA>,
ferlandl at ERE.UMontreal.CA ("Ferland Louis H.") wrote:
> > When I teach this in my Genetics class, I refer to the DNA strand with
> > the same sequence as the mRNA as the sense strand, and the other DNA
> > strand (which is complementary to the mRNA) as the template strand.
> > The students rarely get confused by this nomenclature, as it reflects
> > the actual functions of the two strands.
> > Joanne Tornow
> > University of Southern Mississippi
> Unfortunately (I side with Dr. Lasky), I think you are teaching a wrong
> definition of "sense". They may not be confused in your class and answer
> your exam questions as per what they were taught, but most textbooks
> seem to disagree (see Lasky's previous posting).
> We've got to fix this! Of course, we could decide to adopt this definition
> of "sense" as the strand which, when read by a polymerase, generates a
> non-sensical RNA. I'm being the devil's advocate here (no offense intended),
> just to show that the term is INTRINSICALLY confusing. I'd rather avoid it
> completely when referring to DNA and reserve it for RNA only. See my
> previous posting.
With one correction: "sense" strand in this definition normally IS NOT
BEING transcribed and in the cases when it is really being transcribed,
the resultant RNA is not 'non-sensical', but 'antisensial' and bears
defined regulatory function (like in the case of RNA transcribed from Pout
of IS10 in Tn10. It is involved in regulation of transposition), so
confusion is rather artificial.
If students get the concept of antiparallelity of DNA synthesis right,
then this should not present any difficulty: sense DNA--> antisense RNA;
antisense DNA-->sense RNA. Just like math:
+ x - = -
- x - = +
with transcription process being equivalent to multiplication by negative
(BTW, transcription IS multiplication in biological sense of the word).
If one needs to figure out what DNA strand is being used as a template to
produce, say, anisense RNA (s)he has to divide: -/- = +. In this example
first "-" means "anti" in anisense RNA and the second "-" means copying.
Division is used insted of multiplication since we deduce nature DNA
sequence from RNA, the process reverse to transcription (and in math
division is operation reverse to multiplication).
If one needs to know which strand of DNA has sequence identical to RNA,
there is no need for any operation:
antisense DNA = antisense RNA
sense DNA = sense RNA
What I like in the Joanne Tornow's definition is that "sense" strand does
make sense (meaning that it carries information about what really does
make a difference in the cell: structural RNA and proteins wereas
template (anisense) strand does not normally make any of it. In the case
of antisense RNA the antiparallel strand of DNA (antisense) does make a
difference since it carries information about antisense RNA (it is being
sense for antisense).
The only potential problem with this definition is that, apparently,
GenBank deposit sequences for "sense" strands in the case of proteins and
(at least, in many cases) "antisense" strands for structural RNA.
Just an opinion open to criticism.
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