The Caenorhabditis elegans single tropomyosin gene,
tmy-1 /
lev-11 encodes four isoforms- CeTMI, CeTMII, CeTMIII and CeTMIV. CeTMIII and CeTMIV are expressed in pharynx and gut via alternative splicing by the use of internal promoter of
tmy-1 while the other two isoforms are expressed in body wall, anal and sex muscles under the control of the external promoter. CeTMIII is further expressed in germ-line tissue. Mechanisms and transcription factors involved in production of these isoforms are unknown. Transcription factors such as
pha-4 and
ceh-22 regulate pharyngeal genes expression, and
end-1 ,
elt-2 ,
med-1 and E (capital Eth, Icelandic) 2 associate with gut expression. PHA-4 and CEH-22 control pharyngeal expression of
myo-2 by targeting B and C subelements in its promoter. Similar to
myo-2 , internal promoter of
tmy-1 contains B and C subelements. It is of immense interest to know how PHA-4 involves in the transcription from the internal promoter of
tmy-1. PHA-4 and other transcription factors cooperate to activate transcription of pharyngeal genes. Although these factors have been reported in other cells, none had been identified to associate with intestinal tropomyosin expression. In this study, screening C. elegans cDNA library by yeast one hybrid system using the internal promoter of
tmy-1 as a bait,
egl-4 , a cyclic-guanine monophosphate dependent protein kinase and
egl-18 , a GATA transcription factor were identified. Exons 5a, 5b and 5c of
tmy-1 has
ges-1 -like element. The C. elegans
ges-1 gene encodes a non-specific (with respect to substrate) carboxylesterase normally restricted to the gut. The presence of ges -1 elements in CeTMIII and CeTMIV contributed to their further expression in the intestines. Reporter genes deficient in exons 5a or 5c may be expressed in pharynx only.