subject. "of _____" is a prepositional phrase.

But generally speaking "a lot" can typically use "is" or "are". When "a lot" is referring to a plural, then use "are" e.g. There are a lot of cars on the road today. But when used with a singular noun with a not easily defined quantity, then we use "is". e.g. There is a lot of water on the lawn.

Then again, I may have this wrong. But this is my understanding of this grammar issue.