... in populations. Therefore, when they integ-rate into the host genome, there is little or no selection for maintaining endonuclease function. Moreover, ifthere is any cost to the host cell for ... DNAChemically synthesized DNA fragments, which consist of 18, 20, or 24 nt symmetrically spanning the alpha introninsertion point of the C. reinhardtii COB gene, were clonedinto the EcoRV site of the pCITE-4a ... transmission. Regular invasionaltransmission is likely essential for both homing intronsand inteins. In fact, for the target site of intein homingendonuclease PI-SceI, which is found in Saccharo-myces...