Differential expression of gamma-aminobutyric acidA receptor subunits.
A 1.8-kilobase (kb) cDNA clone for a beta 1 subunit of the human gamma-aminobutyric acidA (GABAA) receptor has been isolated and sequenced. The longest open reading frame of the clone, pCLL610, contains nucleotide sequence encoding a portion of the putative signal sequence followed by 449 amino acids of the entire mature protein. The deduced amino acid sequence of pCLL610 differs from a recently described human beta 1 subunit by a single amino acid. The amino acid sequences of the human GABAA receptor beta 1 subunits share 98% identity with the beta 1 subunits of the bovine and rat GABAA receptor, with the majority of the differences occurring in the intracellular loop between the M3 and M4 transmembrane regions of the protein. A single 11-kb transcript is observed in Northern blots of poly(A)+ RNA isolated from rat brain probed with nick-translated pCLL610. In human brain, the pCLL610 probe recognized the 11-kb message, in addition to two other bands between 8 and 11-kb. Developmental studies of rat brain mRNA show that the message of the GABAA beta 1 subunit is highest at birth, rapidly decreases, and reaches adult levels of 5 to 7 days of age. This is in contrast to the development of the alpha 1 subunit, which is low from days 1 to 5 and increases to adult levels by days 14 to 25. Relative levels of the mRNA for the alpha 1 and beta 1 subunits vary among rat brain regions. The levels of mRNA for the alpha 1 subunit are similar in the cortex, hippocampus, and midbrain, whereas cerebellar levels are twice those in the cortex. The rank order of the relative amount of beta 1 subunit message is hippocampus greater than cortex = midbrain greater than cerebellum. These data, taken with our previous study of the alpha 1 subunits of the GABAA receptor, suggest that the differences in the distribution and regulation of the alpha 1 and beta 1 subunits may reflect a variety of subunit combinations forming the GABAA receptor. Heterogeneity in the GABAA receptor composition may provide a molecular basis for the diverse pharmacological properties associated with this receptor.
Garrett
K M
KM
Department of CNS Biology, American Cyanamid Company, Pearl River, New York 10965.
Saito
N
N
Duman
R S
RS
Abel
M S
MS
Ashton
R A
RA
Fujimori
S
S
Beer
B
B
Tallman
J F
JF
Vitek
M P
MP
Blume
A J
AJ
D000375:Aging; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000254:growth & development* / Q000378:metabolism; D005786:Gene Expression Regulation; D015723:Gene Library; D006801:Humans; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D015345:Oligonucleotide Probes; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011963:Receptors, GABA-A / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid
D046911:Macromolecular Substances; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D011963:Receptors, GABA-A