Research from the early molecular genetics era that supported protein as the primary carrier of genetic information?
It’s difficult to be convincing with a negative answer, but I venture that the answer to your question is that the idea that protein was the genetic material was not supported by any experiments, but was a supposition based on the conventional wisdom that proteins were more complex and therefore more suited to the job.

I suggest that you should be thinking earlier than bacteriophage and Hershey and Chase. Bacteriophages only came into genetic research after the war, and the Hershey/Chase experiment (1952) was only a rigorous confirmation of the conclusion of Avery et al. in 1944 (mentioned in this Scitable article). The system that Avery et al. used (bacterial transformation) went back to Griffiths in 1928 and must have been the first that allowed any sort of experimentation in this area. And I think it was more a question of working out what was happening than devising an experiment to distinguish between protein and DNA as the genetic material.

To my mind this illustrates something about how science progresses. It is often dependent on advances in technology and changes in the conceptual framework in which scientists work. (Sometimes — e.g. Mitchell’s Hypothesis — it needs the experimental results to change that conceptual framework.) Coming back to the Hershey/Chase experiment, this was performed when the balance of scientific thought had already changed to DNA as the genetic material.

Footnote: It’s earlier than you think

I generated the Google ngram below to put the term you use, ‘molecular genetics’ into historical perspective.



This shows that the term ‘molecular genetics’ was hardly in use at the time of the Hershey–Chase experiment and Watson and Crick’s postulate of the structure of DNA in the early 1950s. I think that this reflects the fact that the concept was not current. The more popular term, ‘molecular biology’ gained currency on the basis of the structural work on DNA and proteins, and the name of the journal in which much of the work was published (Journal of Molecular Biology). The question is assuming a state of science that did not actually exist before the 1950s.