Here's something to help you get started. Notice in the first pass, I grabbed the 3rd record. And in the second pass, I printed the 2nd record.

 
#!/usr/bin/perl

use strict;

my $data_pos = tell DATA;
my $record;

while (my $line = <DATA>) {
    chomp( $line );
    $record = $line if ( $line =~ /^:16R:USECU/ );
}

seek DATA, $data_pos, 0;

while (my $line = <DATA>) {
    chomp( $line );
    print "$line\n" if ( $record && $line =~/^:16S:GENL/ );
}

__DATA__
:16S:LINK
:16S:GENL
:16R:USECU
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