I would like to generate a conditional knockout of my protein of interest in a mammalian cell line using the loxP-Cre recombinase system. I have looked at the protein structure and gene structure to decide which exon to flank with the loxP sites for conditional deletion. However, the exon that encodes the essential function of the protein (and would be my preferential exon to target) is 4.9kb, with the introns flanking it being between 2.5 and 3.5 kb. I don't have any experience with the Cre-recombinase system, hence my most pressing question right now: is 4.9kb too large to be efficiently excised with the Cre-recombinase system?