Why is this sentence a complete sentence?

Question

"He and others find that these mRNA's direct,in large part,the synthesis of histones, a class of proteins that bind to DNA. "

It seems to me that perhaps the main verb is "is" (mRNA is direct). But I don't see a connection like a preposition between "mRNA's direct" and "the synthesis of histone". Also, there is a "is" - "mRNA's ", so I assume direct couldn't be a verb.

I can understand there are a subject, a main verb, and a main object. Seems everything is in there. But this sentence still seems weird to me. Why is this sentence a complete sentence? "mRNA's direct the synthesis of histones" : Looks weird to me.

Source: https://science.sciencemag.org/content/206/4416/315 Or you may view the below screenshot if it can not be zoom in.

Answer 1

"In large part" is an idiomatic way of saying 'mostly'.

When a phrase is enclosed in parenthetical commas, as this is, you should be able to read the sentence without it and it make grammatical sense. Let's also take the explanation of histones as being parenthetic and look at the sentence now:

He and others find that these mRNA's direct the synthesis of histones.

The sentence is perfectly grammatical.

That isn't to say that the parenthetical information should be ignored - it is important to the statement that these findings were only correct in the main. The explanation of what histones are is presumably also useful, unless the reader already knows this information.

Note that the apostrophe in "mRNA's" does not denote a possessive or a contraction. Apostrophes are sometimes used to separate the 's' when the plural is an initialism. This is to avoid any confusion that the 's' might be part of it. That is especially useful when the abbreviation contains both upper and lower case characters, as mRNA does.