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From: mikey@bambam.WELLESLEY.EDU (Heather Corbett)
Newsgroups: sci.bio
Subject: Re: Honeycombs and mRNA
Message-ID: <12826@bambam.WELLESLEY.EDU>
Date: 7 Apr 90 01:44:00 GMT
References: <19792@eerie.acsu.Buffalo.EDU> <1209@ccadfa.adfa.oz.au> <7074@uhccux.uhcc.hawaii.edu> <19891@eerie.acsu.Buffalo.EDU> <5029@ucrmath.UCR.EDU> <232@zds-ux.UUCP>
Reply-To: mikey@bambam.UUCP (Heather Corbett)
Organization: Wellesley College
Lines: 23


	This has nothing to do with honeycombs. However, it does have to
do with DNA. Some resistance genes are on plasmids, which are double-stranded
tiny circular chromosomes that occur within E. coli and most likelt other
bacteria. Those plasmids can be used in experiments to confer antibiotic
resistance on a previously susceptible strain of bacteria. In fact, this is
a very useful tool for recombinant work - you put the gene you want on the
plasmid, leaving the resistance gene intact. The most widely used plasmid is
only about 4.5 kD long, remember; the smaller, the easier it is to get into
the cell. Now, if you want to weed out those cells that did NOT take up
the gene you wanted to insert, you culture the bacteria on plates with
medium containing the antibiotic that the plasmid confers resistance to.
Pretty clever, hm?
	Now, what I am skeptical about is muscle cells taking up mRNA. There is
not any good reason that I can think of that a cell would be given a signal
to manufacture mRNA for another cell. Eukaryotes (like humans) do not have
plasmids, so if anything were transfered it would be mRNA transcripts, but
why? Besides, mRNA in the laboratory is extraordinarily fragile and difficult
to work with - for one thing, it is single-stranded... very easy to break.
If indeed human cells "took up" mRNA for one reason or another, what is the
mechanism by which it enters the cell? _In_vitro_ it is very hard to get
cells to take up foreign genetic material.
	Curiously, Heather