To test whether the cosmid DNA contained human homologs of the
rat GluR genes, partial sequence of subcloned fragments of cosmids
containing sequences hybridizing to the homologous rat cDNA probe
was obtained. DNA sequence of introns was also obtained from the
subclones and used as primers for polymerase chain reactions, thereby
avoiding cross-reactivity with the endogenous hamster gene. Subcloning
was accomplished as follows. For GluR 1, cosmid DNA was sonicated
and blunt ended with Klenow and T4 DNA polymerases, and DNA
fragments approximating 250-500 base pairs (bp) were isolated by agarose gel electrophoresis and eluted using a kit from Gene Clean. These
fragments were ligated into an SmaI site of the M 13mp9 vector and
used to transform competent cells. Recombinants containing coding
sequence were identified by hybridization to rat GluRl cDNA. For
GluR2 and GluR3, cosmid DNA was digested with EcoRI and Hind111
restriction endonucleases, separated by electrophoresis on agarose gels,
transferred to filters, and hybridized to radiolabeled probes for the respective rat cDNAs. Fragments (258 and approximately 900 bp for
GluR2 and GluR3, respectively) that hybridized were eluted from agarose gels as above and subcloned into pBluescript KS( +) vectors digested
with EcoRI and HindIII. For GluR4, a 1.8 kbp EcoRI fragment which
hybridized with radiolabeled GluR4 cDNA was subcloned into
pBluescript(+). Plasmid DNA was isolated and digested with BamHI
restriction endonuclease, and the vector with the remaining 1.2 kbp
insert was ligated and used to transform competent cells
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