Because the first 20-nt of the guide RNA corresponds to the target DNA sequence, the beginning of the guide RNA differs between constructs. An ideal 5' self-cleaving ribozyme sequence would be independent of the target sequence. However, all known ribozymes either require certain conserved sequences downstream of the cleavage site, or the sequence of the ribozyme upstream of the cleavage site needs to be altered according to the target sequence. Among those, hammerhead ribozymes (HH ribozymes) offer the best independence of the sequence downstream of the cleavage site.
In the design above, no requirements are placed on the guide RNA sequence. Only 6 nucleotides in the beginning of the hammerhead region need to be modified according to the target sequence.