During large scale sequencing projects where the genome is cloned into e.g. BACs prior to being subcloned into sequencing vectors it is generally the case that the ends of the DNA from one BAC will overlap that of two other BACs. Unless it is being used for quality control, it is a waste of time to sequence the overlapping regions twice, and so most labs transfer the relevant data between the adjacent gap4 databases. This is the function of copy_reads which copies readings from a "source" database to a "destination" database.
The consensus sequences for user selected contigs in each of the two databases are compared in both orientations. If an overlapping region is found, readings of sufficient quality are automatically assembled into the destination database. In the source database readings which have been added to the destination database will be tagged with a "LENT" tag and the equivalent readings in the destination databse will be tagged with a "BORO" (borrowed) tag.