Is this a proper use of a semicolon?

I believe this actually requires a colon and some other punctuation. I see that overexpressed has a lot of precedence in the field.

As an example consider Myc: when overexpressed, it can be a powerful promoter of uncontrolled cell division, yet without accompanying anti-apoptotic mutations, induces cell death.

As far as your question about breaking it into two sentences, I'd say no (you could of course). Technical writing, if it's clear, can benefit a (SME) reader for it to be doled out in larger, but still manageable chunks of information, particularly when the parts interrelate so closely as they do here.

And I don't know what it is, but I do like saying "anti-apoptotic mutations".

I would use a full colon there because the second part is an elaboration of the first statement.

As far as I can tell, you're using an appositive, albeit a long one, and those are properly set off with colons.

Some sports are played on a field; chief among them is the US's national pastime: baseball.

In your example, Myc functions like pastime and the rest functions like baseball.

And although it's not what you asked about, I'd personally drop the "As an example," and start with

Consider Myc: when overexpressed, it can be a powerful promoter...

I would also consider dropping the passive voice: ("promotes" rather than "is a promoter"), which would also create symmetry with "induces."

For less formal writing, I might be tempted to use a dash in place of the colon.

• http://englishplus.com/grammar/00000100.htm
• http://www.grammar-quizzes.com/punc-examples.html