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From: dd@a.UUCP (Dan Davison)
Newsgroups: sci.bio
Subject: Urkaryotes, a correction
Message-ID: <269@a.UUCP>
Date: Thu, 20-Aug-87 19:11:05 EDT
Article-I.D.: a.269
Posted: Thu Aug 20 19:11:05 1987
Date-Received: Sat, 22-Aug-87 12:14:50 EDT
Organization: Los Alamos Natl Lab, Los Alamos, N.M.
Lines: 32
Keywords: they're not really still around

A while back (two months or so) I mentioned in a posting on another
matter that the urkaryotes are still with us, that is, we is them.
That is incorrect and comes from remembering the last half of a sentence
in a paper rather than the first half.

For those who came in late, it has been proposed (Woese and Fox, PNAS
74(11):5088-5090 1977, and J. Molecular Evolution 10(1):1-6, 1977) that
the eucaryotic cytoplasm represents a line of descent that is separate from
the typical bacterial line.  This is now known to workers in the ribosomal
RNA field as the "Three kingdoms"- archebacteria (salt and high temperature-
loving anuclear cells), eubacteria (the cells meant by the word "bacteria")
and eucaryotes.  This division is based on analysis of small ribosomal 
subunit RNAs (the 16S-like rRNAs) that clearly shows three distinct
branches. [Oops, the archaebacteria also include methanogens.]  

When the subject came up last time around I made a comment that the urkaryote
was still around-it's our eucaryotic cell.  As you can guess, that's half
right.  The urkaryote is the source of the eucaryotic cytoplasm, "an ameboid
anaerobic entity free of organelles and the like" (JME reference, pg. 5).
If you've been  reading this newsgroup, organisms mentioned by "baby doc"
werner and myself in recent postings fit some of these requirements.

The point left open by the papers is...did the urkaryote have an 
enveloped genetic material (nucleus)?  If you've read Margulis and
Sagan's _The Origins of Sex: Three Billion Years of Genetic Recombination_
you'll have your own ideas about this one.

Anyone care to speculate, based on knowledge of appropriately weird
organisms?

dan davison/theoretical biology/t-10 ms k710/los alamos national lab/los
alamos NM 87545/ dd@lanl.gov (arpa) / uucp: ...cmcl2!lanl!dd (maybe)