Complex sentence: They found that bacteria respond to an invading phage by transcribing spacers and palindromic DNA into a long RNA molecule that the cell then uses tracrRNA and Cas9 to cut it into pieces called crRNAs.
Split into simpler sentences: They found that bacteria respond to an invading phage by transcribing spacers and palindromic DNA into a long RNA molecule. The cell then uses tracrRNA and Cas9 to cut this long RNA molecule into pieces called crRNAs.