genetic engineering

So in the book it says 'vectors often have to contain regulatory sequences of DNA. These ensure that the inserted gene is transcribed in the host cell'.

Why does there have to be a regulatory sequence of DNA? Doesn't the regulatory sequence just code for a repressor protein which just stops the protein being transcribed? That doesn't make any sense :s-smilie:

(edited 11 years ago)

Reply 1

onefour

9

There are several different types of regulatory sequences, not just repressors. In this context, it refers to promoter elements where the RNA polymerase binds to initiate transcription. Promoter sequences are different in eukaryotes and prokaryotes so it is necessary to engineer in the vector-specific promoter to the inserted gene so the vector proteins can recognise it.

Reply 2

username1003420

OP

20

Original post by onefour

There are several different types of regulatory sequences, not just repressors. In this context, it refers to promoter elements where the RNA polymerase binds to initiate transcription. Promoter sequences are different in eukaryotes and prokaryotes so it is necessary to engineer in the vector-specific promoter to the inserted gene so the vector proteins can recognise it.

So basically having the regulatory sequence there makes it more likely for the gene to be switched on? But then again, wouldn't it be more likely for the gene to be transcribed if the gene didn't need to be switched on or off?

Reply 3

onefour

9

Original post by tammie123

So basically having the regulatory sequence there makes it more likely for the gene to be switched on? But then again, wouldn't it be more likely for the gene to be transcribed if the gene didn't need to be switched on or off?

The promoter sequence has to be present because it is the part of the DNA sequence that the RNA polymerase binds to - if there was no promoter, RNA polymerase wouldn't bind and the gene wouldn't be transcribed (or 'turned on'). Sometimes when a gene is inserted into a vector, additional regulatory sequences such as repressors are removed so that expression is constitutive (i.e. the gene is constantly expressed/doesn't need to be switched on or off). Hopefully that makes sense.

Reply 4

username1003420

OP

20

Original post by onefour

The promoter sequence has to be present because it is the part of the DNA sequence that the RNA polymerase binds to - if there was no promoter, RNA polymerase wouldn't bind and the gene wouldn't be transcribed (or 'turned on'). Sometimes when a gene is inserted into a vector, additional regulatory sequences such as repressors are removed so that expression is constitutive (i.e. the gene is constantly expressed/doesn't need to be switched on or off). Hopefully that makes sense.

Oh so regulatory sequences always have to be present, but then why does the book say 'vectors often have to contain regulatory sequences of DNA'? So does that mean that sometimes it's not needed?

Sorry for all the questions, I'm just really confused.

(edited 11 years ago)

Reply 5

onefour

9

Original post by tammie123

Oh so regulatory sequences always have to be present, but then why does the book say 'vectors often have to contain regulatory sequences of DNA'? So does that mean that sometimes it's not needed?

Sorry for all the questions, I'm just really confused.

Regulatory sequences such as promoters are always required but other regulatory elements like repressors are not always engineered in as not every inserted gene will need them.

Reply 6

StudyingHelp

10

Original post by onefour

The promoter sequence has to be present because it is the part of the DNA sequence that the RNA polymerase binds to - if there was no promoter, RNA polymerase wouldn't bind and the gene wouldn't be transcribed (or 'turned on'). Sometimes when a gene is inserted into a vector, additional regulatory sequences such as repressors are removed so that expression is constitutive (i.e. the gene is constantly expressed/doesn't need to be switched on or off). Hopefully that makes sense.

Don't you mean DNA polymerase (Only asking because the book mentions it) ?

Reply 7

onefour

9

Original post by StudyingHelp

Don't you mean DNA polymerase (Only asking because the book mentions it) ?

No - I am talking about transcription, not DNA replication. DNA polymerases don't bind transcription promoters.

Reply 8

rival_

10

The regulatory gene, codes for transcription factors. These can be repressors - e.g. in lac operon, or they can actually encourage protein transcription through working as activators e.g. - cAMP.

Reply 9

Ashnard

14

Original post by tammie123

Oh so regulatory sequences always have to be present, but then why does the book say 'vectors often have to contain regulatory sequences of DNA'? So does that mean that sometimes it's not needed?

Sorry for all the questions, I'm just really confused.

Not all vectors contain DNA inserts that have to be expressed. Cloning vectors, which contain DNA fragments to be sequenced, don't need to express the inserted fragment. Those vectors that express the DNA insert, called expression vectors, must contain some promoter sequence so that the insert can be expressed.

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