[BioC] assemble DNAString complete coding sequence from exons?

[Paul Shannon]

I am sure there is an elegant way to do this.  Could somebody clue me  
in?

I have (in a simple case) two exons for a gene on the + strand, and a  
the full DNAString sequence of its chromosome.

My naive technique for constructing a DNAString of the entire coding  
sequence is

   1) paste together toString (subseq (seq.chrom, exon.start,  
exon.end)) for each exon
   2) construct a DNAString from the resulting chars.

There must be a better way.  What is it?

Thanks!

  - Paul