I am having trouble with cloning. My PCR product is 1.7kb with EcoRI and SalI site at both ends. After ligation into the plasmid, I transformed into E. coli DH5alpha cell. The colonies growth slowly. I did the colony PCR for searching the candidate with the Forward primer which is anneal to the middle of the insert and the reverse primer which is anneal to the vector and I got the candidate colony. I purified the plasmid from these candidates and did restriction enzyme with the same enzyme for checking. But the insert from the digestion is 1.5kb, shorter than before ligation. Do you have any ideas about this situation? I did it for three times and the results were the same. What should I do next?
Thank in advance.