I have problem when I want to PCR 16sr RNA gene of my unknown strain. I have extracted its DNA and did PCR by using lyophilized master mix tube for PCR. The result was good but I had an extra band in my gel electrophoresis. I did the PCR again but the problems exist. So I extracted the DNA by using another Kit and did PCR with another PCR pack. But the result was not good. I think my problem is in mastermix preparation or in my thermal program. Can anyone give me an advice to solve this problem?