Molecular cloning of a myosin I beta isozyme that may mediate adaptation by hair cells of the bullfrog's internal ear.
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.
Metcalf
A B
AB
Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas 75235-9117.
Chelliah
Y
Y
Hudspeth
A J
AJ
D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D001921:Brain / Q000201:enzymology; D002417:Cattle; D003001:Cloning, Molecular; D017124:Conserved Sequence; D017931:DNA Primers; D015870:Gene Expression; D006199:Hair Cells, Auditory, Inner / Q000201:enzymology / Q000502:physiology*; D007527:Isoenzymes / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D009218:Myosins / Q000096:biosynthesis*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000302:isolation & purification / Q000378:metabolism; D011892:Rana catesbeiana; D051381:Rats; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D007527:Isoenzymes; D012333:RNA, Messenger; D009218:Myosins