I think it's evolution that made eukaryotic machinery smaller and smarter.

I think the reason is speed. Synthesis of Okazaki fragments in eukaryotes is rate limiting when compared to prokaryotes, which justifies the length of these fragments.

Thank you all for your feedback,

I think it is both an evolutionary process and speed etc. But the more specific reason appears to be association of histonic octamer. I observed that the size of Okazaki fragments is similar to the lenth of mono nucleosome DNA, that is approximately 200bp and I suppose that both are co-evolved. May be in one round, only one mono-nucleosome is "unwrapped", the okazaki fragment is thus formed till that lenght and so on.

When I was searching for the answer, I came to know that in Prokaryotes, the DNA replication is linked to cell cycle. Hence, suppose the cell has to divide in 30 minutes, the DNA also should be replicated within that limit. Hence, since the Okazaki fragment turnover is a rate limiting kind of step (slow process) the cell cant afford smaller fragment size and has to synthesize larger fragment in order to match up the speed.

I may be wrong, but I am just learning.

Amended on 11 February 2018 (Today, it is said that Japan has been established for 2678 years ago)

My opinion is that eucaryote, procaryote, and virus have started to live at possibly 3,600,000,000 years ago, and procayote (bacteria) and virus have triumphed over eucaryote. Therefore, mechanisms for protein synthesis and DNA synthesis are different between eucaryote and procaryote. Avidin (chicken) is very different in amino acid sequence from procaryotic Streptavidin.

I have studied about the DNA replication issue by using PDMD method (please see file; HepG2 fucoidan).

HCC (Cancer) HepG2 cells have DNA polymerase alpha catalytic subunit at 2.6 μg/mg of cell protein, but healed HepG2 and normal fetal Hc cells have no DNA replication enzymes.

There are unexpectedly no differences between HCC and LC liver tissues. HCC tissue (with PBC) also has no DNA replication enzyme. Normal liver tissue (Pseudo-liver cancer) has DNA topoisomerae II, beta isozyme at 9.8 μg/mg of tissue protein.

LC tissue (with leprosy) has DNA polymerase alpha catalytic subunit at 2.8, DNA polymerase epsilon, catalytic subunit at 4.1, and DNA topoisomerase I at 7.3 μg/mg of tissue protein, respectively (total machinery proteins becomes to 14.2 μg/mg of tissue protein).

LC tissue (named as No.6) has DNA primase large subunit at 10.2 μg/mg of tissue protein. HCC tissue (named as No.6) has DNA ligase I at 5.2 μg/mg of tissue protein and DNA polymerase epsilon catalytic subunit at 3.9 μg/mg of tissue protein (total machinery proteins becomes to 9.1 μg/mg of tissue protein.

Therefore, there is no significant differences in the amount of the DNA replication machinery between LC + Normal (Pseudo-liver cancer) and HCC (cancer) (NS; n1=5, n2=3; Mann-Whitney's U test).

Procaryote of Lactobacillus casei (Shirota) has DNA topoisomerase III at 10.0 μg/mg of cell protein.

Therefore, procaryote seems to have higher amount of DNA replication machinery than normal eucaryotes.