Attenuated function of a variant form of the helix‐loop‐helix protein, Id‐3, generated by an alternative splicing mechanism

Abstract

The Id family of helix‐loop‐helix proteins function as negative regulators of DNA binding, basic helix‐loop‐helix proteins in the regulation of cell growth and differentiation. We report here on the identification of a 17 kDa variant of the 14 kDa Id‐3 protein termed Id‐3L (long version) which possesses a unique 60 amino acid carboxy‐terminus generated by readthrough of a ‘coding intron’ and alternative splicing. Northern analysis revealed expression of a minor 1.1 kb Id‐3L transcript together with the predominant 0.95 kd Id‐3 transcript in the majority of adult human tissues analysed. The variant Id‐3L protein is functionally distinguishable from conventional Id‐3 since in in vitro DNA mobility shift assays, it was greatly impaired in its ability to abrogate binding of the basic helix‐loop‐helix protein, E47, to an E box recognition sequence.