Comparison of initiation of DNA replication with transcription initiation
The initiation of DNA replication has also been compared with transcription, due to many similarities : (i) both involve ordered protein-DNA and protein-protein interactions leading to site identification and positioning of appropriate polymerase at this site; (ii) transcriptional promoters are heterogeneous regulatory elements and so are replication origins; (iii) promoters have common core elements, where basic transcription factors bind; replication origins also have core consensus sequences for binding of recognition factors like ORC; (iv) promoters have flanking sequences besides core elements; accessory factors binding on these flanking sequences, modulate the activity of basic transcription factors and thereby regulate the rate of transcription initiation in response to a variety of stimuli; at replication origins also there are 'accessory control elements' (e.g. B₃ at ARS1) or 'auxiliary elements', where trans-acting factors bind and modulate the activity of the replication origin. Since transcription factors are involved both in transcription and replication, they may play an important role in. temporal coordination of transcription and replication during the cell cycle (Fig. 26.26).