In the brain, dopamine and adenosine stimulate cyclic AMP (cAMP) production through D1 and A2a receptors, respectively. Using mutant mice de®cient in the olfactory isoform of the stimulatory GTP-binding protein a subunit, Ga olf , we demonstrate here the obligatory role of this protein in the adenylyl cyclase responses to dopamine and adenosine in the caudate putamen. Responses to dopamine were also dramatically decreased in the nucleus accumbens but remained unaffected in the prefrontal cortex. Moreover, in the caudate putamen of mice heterozygous for the mutation, the amounts of Ga olf were half of the normal levels, and the ef®cacy of dopamine-and CGS 21680 A 2 agonist-stimulated cAMP production was decreased. Together, these results identify Ga olf as a critical parameter in the responses to dopamine and adenosine in the basal ganglia.

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Focal adhesion kinase (FAK) is activated following integrin engagement or stimulation of transmembrane receptors. Autophosphorylation of FAK on Tyr-397 is a critical event, allowing binding of Src family kinases and activation of signal transduction pathways. Tissue-specific alternative splicing generates several isoforms of FAK with different autophosphorylation rates. Despite its importance, the mechanisms of FAK autophosphorylation and the basis for differences between isoforms are not known. We addressed these questions using isoforms of FAK expressed in brain. Autophosphorylation of FAK ؉ , which is identical to that of "standard" FAK, was intermolecular in transfected cells, although it did not involve the formation of stable multimeric complexes. Coumermycin-induced dimerization of gyrase B-FAK ؉ chimeras triggered autophosphorylation of Tyr-397. This was independent of cell adhesion but required the C terminus of the protein. In contrast, the elevated autophosphorylation of FAK ؉6,7 , the major neuronal splice isoform, was not accounted for by transphosphorylation. Specifically designed immune precipitate kinase assays confirmed that autophosphorylation of FAK ؉ was intermolecular, whereas autophosphorylation of FAK ؉6,7 or FAK ؉7 was predominantly intramolecular and insensitive to the inhibitory effects of the N-terminal domain. Our results clarify the mechanisms of FAK activation and show how alternative splicing can dramatically alter the mechanism of autophosphorylation of a protein kinase.