Complex sentence: Since the two reverse complementary sequences will fold and attach with each other, the sequence of bases between them form a hairpin loop which is thought to destabilize the binding of RNA polymerase enzyme to DNA (hence terminating transcription).
Split into simpler sentences: Since the two reverse complementary sequences will fold and base-pair with each other, the sequence of bases between them form a hairpin loop. This structure is thought to destabilize the binding of RNA polymerase enzyme to DNA (hence terminating transcription).