Final answer:
When RNA polymerase II leaves the promoter to begin elongation in eukaryotic cells, certain basal transcription factors dissociate from the complex, enabling RNA polymerase II to proceed with elongation.
Step-by-step explanation:
The factors that do not stay behind the scaffold when RNA polymerase II leaves the promoter to begin elongation in eukaryotic cells are the basal transcription factors involved in the formation of the preinitiation complex. Initially, a series of transcription factors called TFII factors (TFIIA-J) and RNA polymerase II form a complex with the DNA template to initiate transcription.
Once RNA polymerase II is appropriately positioned and phosphorylated, certain transcription factors may dissociate from the complex, allowing RNA polymerase II to proceed with the elongation phase, synthesizing pre-mRNA in the 5' to 3' direction.