Undergraduate in Computer science and now graduate in Bioinformatics I am a computer engineering undergrad (from Asia) and now trying to pursue my graduate studies in bioinformatics (in US). I have quite a strong programming skills and now more than one year of experience too. Since I do not have a strong background of biology, is it good to choose that field? Also, I have been doing some research to get any assistantship (have applied to few colleges) but could not start a communication with the professors. How should I approach?

Any help would be great to me.
There are a number of bioinformatics programs that do not require you to have experience in both programming and biology. For example, the program at BU

What if I don’t have experience in both computational and experimental fields?
Applicants are not required to be well versed in both fields. Even if you do not have the academic background in both the computational and experimental fields, we are looking for highly motivated students

So only having a programming background should not be too much of a problem. You will probably want to have picked up and had a look at some undergraduate biology texts so that you are not completely clueless about the field.
As for approaching professors, it really is no different from other fields. Applicants to graduate school, whether for a PhD or a Masters, don't have all the skills to carry our independent research in the field. To get a research assistantship you need to find professors who are doing research that is interesting to you and send them your CV along with a well written email expressing why you want to work with them, what skills you bring with you, and what you want to learn. There are a number of related question on AC.SE that can help you in this regard.