Well, depending on how broad your definition of life is, viruses have the most stripped down genomes of all. In the smallest viruses, with genomes of just under 10kb in length, nearly every basepair is dedicated to either infection or replication. In fact, they are often so compact that open reading frames are interleaved, in order to provide more functionality without increasing size.

Scientists often refer to viruses as "obligate", in order to sidestep the question of what is life, as most have no interest in the topics which occupy philosophers. In any case, they are non-cell based, for whatever that is worth. I imagine in a non-hostile environment, even the infection functional would be shed, and you would be left with just replication, which is the fundamental component beyond which no further reduction in complexity can be made.