This is really a “chicken or egg” question that cannot be answered in any objectively correct way. I would argue, however, that in the long run, political culture ends up affecting government more than the other way around.
In some ways, the government affects political culture. For example, when the US imposed a new constitution on Japan after WWII, it changed their political culture. It made them into much more of a democracy than they had been. This helped to bring about a change in their political culture that, for example, made political dissent much more acceptable.
However, it seems to me that political culture ends up having more of an impact on government. Our country would not have been set up with the Constitution that it has if it were not for the fact that there was a strong republican and libertarian political culture already existing in the colonies. Our states also have different governmental policies (think about the death penalty here) depending on the different political cultures of the states.
Thus, I would argue that the political culture has more of an impact on the government than vice versa, but this is not something that I can objectively prove.