The Russian-American biochemist Phoebus Levene was the first to determine that nucleotides may contain one of four different nitrogen-containing bases. Levene believed that the nitrogen-containing bases occurred in equal amounts in DNA. What is the actual proportion of these bases?

It depends on the specimen

Step-by-step explanation:

The actual proportion of this bases depends a lot on the organism and the molecule, but it is mostly 60-40 and importance of it is that the purines need to be in equal amounts, and the pyramidines as well, so the proportion between purines and pyramidines is mostly 60-40%, but them between adenine and guanine the proportion is 30-30 and between cytosine and thymine should be 20-20.