Formation of chromatin loops at gene loci permits coordination between processes of transcription initiation, termination, and splicing. Promoter and terminal regions of genes colocalize during transcription, forming a looped structure that enhances transcriptional directionality. Gene loop formation depends on contacts between both promoter-associated transcription factors, such as TFIIB, within the pre-initiation complex and polyadenylation factors, such as Ssu72 and cleavage factor subunits, within the terminator complex. Extensive contacts between the spliceosome and the initiating and elongating polymerase II complex also facilitate cotranscriptional splicing.
