The RNA synthesized by RNA polymerase II is known as the transcript. It is later modified into the mature mRNA.

The RNA synthesized by RNA polymerase II is known as the primary transcript. This primary transcript undergoes several modifications to become the mature mRNA.

Step 1: Synthesis of Primary Transcript The process begins with the binding of RNA polymerase II to the DNA at the promoter region. The enzyme then unwinds the DNA and starts synthesizing the primary transcript using one of the DNA strands as a template.

Step 2: Capping Once the synthesis of the primary transcript begins, a modified guanine nucleotide is added to the 5' end of the RNA. This is known as the 5' cap and it helps in the stability of the mRNA and its transportation out of the nucleus.

Step 3: Elongation RNA polymerase II continues to move along the DNA, synthesizing the RNA transcript.

Step 4: Splicing In eukaryotes, the primary transcript contains both coding regions (exons) and non-coding regions (introns). Splicing is the process where the introns are removed and the exons are joined together to form a continuous coding sequence.

Step 5: Polyadenylation Once the RNA reaches the end of the gene, an enzyme adds a series of adenine nucleotides to the 3' end of the RNA. This is known as the poly-A tail and it aids in the stability and export of the mRNA from the nucleus.

Step 6: Export to the Cytoplasm The mature mRNA, now with a 5' cap, a continuous coding sequence, and a poly-A tail, is then exported from the nucleus to the cytoplasm where it will be translated into a protein.