Complex sentence: In Gram-negative bacteria, however, Shine-Dalgarno sequence presence is not obligatory for ribosome to locate initiator codon, since deletion of Anti-Shine-Dalgarno sequence from 16S rRNA doesn't lead to translation initiation at non-authentic sites.
Split into simpler sentences: In Gram-negative bacteria, the presence of a Shine-Dalgarno sequence is not obligatory for the ribosome to locate the initiator codon. For example, it has been shown that deletion of Anti-Shine-Dalgarno sequence from 16S rRNA doesn't lead to translation initiation at non-authentic sites.