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Proc Natl Acad Sci U S A. 1994 Dec 6;91(25):11821-5.

Molecular cloning of a myosin I beta isozyme that may mediate adaptation by hair cells of the bullfrog's internal ear.

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  • 1Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas 75235-9117.


The internal ear's sensory receptor, or hair cell, responds when stimuli deflect its mechanoreceptive hair bundle. As a hair cell adapts to sustained stimulation, mechanical adjustments within the bundle reset its position of sensitivity. Because several lines of experimentation suggest that a form of myosin I mediates adaptation, we endeavored to clone cDNAs encoding this motor molecule. By using degenerate oligonucleotide primers based upon the deduced amino acid sequence for mammalian myosin I beta, we performed reverse transcription and polymerase chain reactions (PCRs) to produce a candidate cDNA from polyadenylylated mRNA isolated from the frog's brain. The resultant product was used to probe a cDNA library, from which were isolated clones encoding an approximately 119-kDa isozyme of myosin I beta. PCR amplification disclosed the presence of mRNA encoding the same isozyme in tissue from the bullfrog's sacculus, an organ of the internal ear. When expressed as a bacterial fusion protein, a domain from the tail region of this form of myosin I was recognized by monoclonal antibodies that react with myosin I in hair bundles. This cloned approximately 119-kDa isozyme of myosin I is accordingly a candidate to be the motor molecule responsible for the adaptation of mechanoelectrical transduction by hair cells.

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