Worm Breeder's Gazette 10(1): 51

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Tc4, a New C. elegans Transposon

J. Yuan, M. Finney and B. Horvitz

Mutator strains isolated on the basis of increased Tc1 transposition 
in Phil Anderson's laboratory have provided a powerful tool to use in 
the molecular cloning of C.  elegans genes.  One can look for mutator-
induced alleles of a gene of interest and then use Tc1 as a probe to 
determine whether Tc1 has inserted into the gene.  One difficulty in 
using this approach has been that not all mutator-induced mutations 
are caused by insertion of Tc1.  We have discovered that two mutator-
induced unc-86 alleles, u371 (isolated by Marty Chalfie) and n1351 (
isolated by Stuart Kim), contain two different kinds of non-Tc1 
insertions.  With the hope of identifying more worm transposons, we 
have cloned both of these insertions.  The insertion in u371 was found 
to be the same as an insertion isolated in Phil Anderson's laboratory; 
this insertion is now called Tc3.  The 1.8 kb insertion in n1351, now 
called Tc4, was found to have also inserted into ced-4 (see abstract 
by Junying Yuan and Bob Horvitz in this WBG).
Southern blot analyses showed that there are about 20 copies of Tc4 
in both the Bristol and Bergerac strains, with a few polymorphisms 
between these strains.  Although we have not examined our parental 
mutator strains for the number of Tc4 copies, one 10x-backcrossed 
mutant generated from mut-2 contains a few extra bands of Tc4, 
consistent with the hypothesis that Tc4 is activated in mut-2.  Tc4 
has a number of properties that indicate that it is a foldback element,
i.e.  it consists of a pair of inverted repeat DNA sequences.  First, 
restriction enzyme mapping showed that Tc4 has symmetrical restriction 
sites.  Second, it inverts its position in a plasmid vector very 
frequently when it is carried in a RecA strain.  Third, presumably due 
to its foldback structure, Tc4 is difficult to label using the 
standard oligo-labelling method unless the element is first cut in the 
middle by a restriction enzyme.  Northern blot analyses have shown 
that N2 expresses at least four poly-A(+) RNAs that can hybridize to 
Tc4.  One is about 5 kb, one is about 3 kb and two are about 1.7 kb.  
The size differences could be due to heterogeneity in the size and 
structure of Tc4 elements because on Southern blots the intensity of 
different Tc4 bands are very different.  We are interested in seeing 
if extra classes of Tc4 transcripts are present in the mutator strains,
and if so whether such transcripts can account for the mutator