Cloning of a newly identified heart-specific troponin I isoform, which lacks the troponin T binding portion, using the yeast hybrid system.
OBJECTIVE
To elucidate the molecular pathogenesis behind increased levels of laminin in cardiac muscle cells in cardiomyopathy by using a yeast hybrid screen. The present study reports the cloning of a newly identified heart-specific troponin I isoform, which is putatively linked to laminin. Future studies will explore the functional significance of this connection.


METHODS
Yeast two-hybrid screen analysis was performed using MLF1-interacting protein (amino acids 1 to 318) as bait. The human heart complementary DNA library was screened by using the yeast-mating method for overnight culture.


RESULTS
Two final positive clones from the heart library were isolated. These two clones encoded the same protein, a short isoform of human cardiac troponin I (TnI) that lacked TnI exons 5 and 6. The TnI isoform has a heart-specific expression pattern and it shares several sequence features with human cardiac TnI; however, it lacks the troponin T binding portion.


CONCLUSIONS
The heart-specific segment of the human cardiac TnI isoform shares several sequence features with human cardiac TnI, but it lacks the troponin T binding portion. These results suggest that the heart-specific TnI isoform may be involved in cardiac development and disease.
Suzuki
Hideaki
H
Departments of Internal Medicine and.
Arakawa
Yasuhiro
Y
Ito
Masaki
M
Yamada
Hisashi
H
Horiguchi-Yamada
Junko
J