Allikmets, Gerrard, Hutchinson, and Dean (1996) characterized a large
number of human ABC transporter genes by searching the human EST
database using sequences derived from ABC (Walker A, ABC signature,
and Walker B) of MDR1, as well as the entire sequence of cystic fibrosis
transmembrane conductane regulator (CFTR). Because many of the ESTs
are derived from brain libraries, the data suggested that many of these
ABC transporters were expressed in brain. Because the number of ESTs
deposited in public databases has increased substantially in the past 4
years, we recently repeated this analysis in order to ensure that the full
complement of brain-expressed ABC transporters was represented in the database. Moreover, to increase the power of our search, we developed consensus
amino acid sequences for the Walker A motif, as well as the ABC signature
and Walker B motifs, by comparing the sequences of the following
human ABC transporters. The consensus sequences
that emerged from this analysis were (G(X)2G(X)GK(X)T(X)4L(X)2L(X)2PT(X)3G
for the Walker A motif, and LSGG(X)4L(X)2A(X)AL(X)3PKV(X)2LDE(X)TS(X)
for the ABC signature and Walker B motifs.
The BLAST programs (Altschul, Gish, Miller, Myers, & Lipman, 1990) were used to search the human database EST using these consensus sequences, as well as the complete amino acid sequences of the human ABC-transporter proteins identified above. Human clones with the highest scores were retrieved and primers were designed using the program Mac Vector (Oxford Molecular, UK). Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed using brain fetal and adult total RNA (Invitrogen) in order to confirm human brain expression, and PCR products were sequenced to authenticate the ESTs.
Based on both the cDNA library source used to generate these ESTs, as well as the expression profile of RNA as seen in Northern blots (Allikmets et al. 1996, and unpublished data), we identified the 14 ABC transporters listed in Table 10.1 as being brain-expressed.
The BLAST programs (Altschul, Gish, Miller, Myers, & Lipman, 1990) were used to search the human database EST using these consensus sequences, as well as the complete amino acid sequences of the human ABC-transporter proteins identified above. Human clones with the highest scores were retrieved and primers were designed using the program Mac Vector (Oxford Molecular, UK). Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed using brain fetal and adult total RNA (Invitrogen) in order to confirm human brain expression, and PCR products were sequenced to authenticate the ESTs.
Based on both the cDNA library source used to generate these ESTs, as well as the expression profile of RNA as seen in Northern blots (Allikmets et al. 1996, and unpublished data), we identified the 14 ABC transporters listed in Table 10.1 as being brain-expressed.
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